Prove $Delta text{ABC}$ is a right triangle?
Prove $Delta text{ABC}$ is a right triangle if:
$$left{begin{matrix} sin^{2},text{A}+ sin^{2},text{B}= sin text{C}\ maxleft { measuredangle text{A}- text{k},measuredangle text{B},,measuredangle text{B}- text{k},measuredangle text{A} right }leqq frac{pi }{2}\ left | text{k} right |leqq 3 end{matrix}right.$$
I have a proof for my problem with $text{k}= 0$. See here:
$lceil$ https://diendantoanhoc.net/topic/185093-measuredangle-textc-pi/#entry716757 $rfloor$
I also have another solution but ugly, I try to use similar method with $left | text{k} right |leqq 3$ but without success !
geometry trigonometry inequality
add a comment |
Prove $Delta text{ABC}$ is a right triangle if:
$$left{begin{matrix} sin^{2},text{A}+ sin^{2},text{B}= sin text{C}\ maxleft { measuredangle text{A}- text{k},measuredangle text{B},,measuredangle text{B}- text{k},measuredangle text{A} right }leqq frac{pi }{2}\ left | text{k} right |leqq 3 end{matrix}right.$$
I have a proof for my problem with $text{k}= 0$. See here:
$lceil$ https://diendantoanhoc.net/topic/185093-measuredangle-textc-pi/#entry716757 $rfloor$
I also have another solution but ugly, I try to use similar method with $left | text{k} right |leqq 3$ but without success !
geometry trigonometry inequality
Do you mean "for all $k$ with $|k|leq3,$" or "for some $k$ with $|k|leq3,$"?
– Christian Blatter
Dec 9 at 11:01
1
I mean for all $text{k}$ ! Thanks !
– HaiDangel
Dec 9 at 12:33
add a comment |
Prove $Delta text{ABC}$ is a right triangle if:
$$left{begin{matrix} sin^{2},text{A}+ sin^{2},text{B}= sin text{C}\ maxleft { measuredangle text{A}- text{k},measuredangle text{B},,measuredangle text{B}- text{k},measuredangle text{A} right }leqq frac{pi }{2}\ left | text{k} right |leqq 3 end{matrix}right.$$
I have a proof for my problem with $text{k}= 0$. See here:
$lceil$ https://diendantoanhoc.net/topic/185093-measuredangle-textc-pi/#entry716757 $rfloor$
I also have another solution but ugly, I try to use similar method with $left | text{k} right |leqq 3$ but without success !
geometry trigonometry inequality
Prove $Delta text{ABC}$ is a right triangle if:
$$left{begin{matrix} sin^{2},text{A}+ sin^{2},text{B}= sin text{C}\ maxleft { measuredangle text{A}- text{k},measuredangle text{B},,measuredangle text{B}- text{k},measuredangle text{A} right }leqq frac{pi }{2}\ left | text{k} right |leqq 3 end{matrix}right.$$
I have a proof for my problem with $text{k}= 0$. See here:
$lceil$ https://diendantoanhoc.net/topic/185093-measuredangle-textc-pi/#entry716757 $rfloor$
I also have another solution but ugly, I try to use similar method with $left | text{k} right |leqq 3$ but without success !
geometry trigonometry inequality
geometry trigonometry inequality
edited Dec 9 at 13:19
asked Dec 9 at 7:19
HaiDangel
213
213
Do you mean "for all $k$ with $|k|leq3,$" or "for some $k$ with $|k|leq3,$"?
– Christian Blatter
Dec 9 at 11:01
1
I mean for all $text{k}$ ! Thanks !
– HaiDangel
Dec 9 at 12:33
add a comment |
Do you mean "for all $k$ with $|k|leq3,$" or "for some $k$ with $|k|leq3,$"?
– Christian Blatter
Dec 9 at 11:01
1
I mean for all $text{k}$ ! Thanks !
– HaiDangel
Dec 9 at 12:33
Do you mean "for all $k$ with $|k|leq3,$" or "for some $k$ with $|k|leq3,$"?
– Christian Blatter
Dec 9 at 11:01
Do you mean "for all $k$ with $|k|leq3,$" or "for some $k$ with $|k|leq3,$"?
– Christian Blatter
Dec 9 at 11:01
1
1
I mean for all $text{k}$ ! Thanks !
– HaiDangel
Dec 9 at 12:33
I mean for all $text{k}$ ! Thanks !
– HaiDangel
Dec 9 at 12:33
add a comment |
2 Answers
2
active
oldest
votes
One idea: Using the formulas $$A=frac{1}{2}absin(gamma)$$ etc we get
$$frac{4A^2}{b^2c^2}+frac{4A^2}{a^2c^2}=frac{2A}{ab}$$ and using $$A=sqrt{s(s-a)(s-b)(s-c)}$$ where $$s=frac{a+b+c}{2}$$ plugging this in our formula we get after squaring and simplifying
$$- left( {a}^{6}-{a}^{4}{b}^{2}-{a}^{4}{c}^{2}-{a}^{2}{b}^{4}-6,{a}^{
2}{b}^{2}{c}^{2}+{b}^{6}-{b}^{4}{c}^{2} right) left( {a}^{2}+{b}^{2
}-{c}^{2} right)
=0$$
it remaines to show that the first factor can not be zero.
add a comment |
If I read the second condition as
$$alpha-kbetaleq{piover2},quadbeta-kalphaleq{piover2}qquad forall >kin[-3,3] ,$$
and add these two inequalities in the case $k:=-3$ I obtain
$$4(alpha+beta)leq pi ,$$
or $alpha+betaleq{piover4}$. I don't see how a right triangle can be formed in this way, even without looking at the first condition. Note that in the linked source they are only talking about the case $k=3$.
1
$left | text{k} right |leqq 3$ is acceptable ! With $left | text{k} right |leqq 3$, for example: $text{A}= 4,text{B}+ frac{5,pi}{11},,text{C}= frac{6,pi}{11}- 5,text{B},,left | text{k} right |= 4Rightarrow text{B}neq frac{pi}{110} Rightarrow text{C}neq pi$ ! I understand your comment & I think $left | text{k} right |leqq 3$ is neccessary for my problem ! $text{k}= 3$ is my original problem, then I generalised it to $left | text{k} right |leqq 3$ , those are all of mine on Vietnamese Math Forum ( Diendantoanhoc.net ) ! Thanks for your interest !
– HaiDangel
Dec 10 at 1:19
1
There are some misunderstandings about my problem here: $lceil$ artofproblemsolving.com/community/c6h1725878p11175691 $rfloor$
– HaiDangel
Dec 10 at 1:29
add a comment |
Your Answer
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
One idea: Using the formulas $$A=frac{1}{2}absin(gamma)$$ etc we get
$$frac{4A^2}{b^2c^2}+frac{4A^2}{a^2c^2}=frac{2A}{ab}$$ and using $$A=sqrt{s(s-a)(s-b)(s-c)}$$ where $$s=frac{a+b+c}{2}$$ plugging this in our formula we get after squaring and simplifying
$$- left( {a}^{6}-{a}^{4}{b}^{2}-{a}^{4}{c}^{2}-{a}^{2}{b}^{4}-6,{a}^{
2}{b}^{2}{c}^{2}+{b}^{6}-{b}^{4}{c}^{2} right) left( {a}^{2}+{b}^{2
}-{c}^{2} right)
=0$$
it remaines to show that the first factor can not be zero.
add a comment |
One idea: Using the formulas $$A=frac{1}{2}absin(gamma)$$ etc we get
$$frac{4A^2}{b^2c^2}+frac{4A^2}{a^2c^2}=frac{2A}{ab}$$ and using $$A=sqrt{s(s-a)(s-b)(s-c)}$$ where $$s=frac{a+b+c}{2}$$ plugging this in our formula we get after squaring and simplifying
$$- left( {a}^{6}-{a}^{4}{b}^{2}-{a}^{4}{c}^{2}-{a}^{2}{b}^{4}-6,{a}^{
2}{b}^{2}{c}^{2}+{b}^{6}-{b}^{4}{c}^{2} right) left( {a}^{2}+{b}^{2
}-{c}^{2} right)
=0$$
it remaines to show that the first factor can not be zero.
add a comment |
One idea: Using the formulas $$A=frac{1}{2}absin(gamma)$$ etc we get
$$frac{4A^2}{b^2c^2}+frac{4A^2}{a^2c^2}=frac{2A}{ab}$$ and using $$A=sqrt{s(s-a)(s-b)(s-c)}$$ where $$s=frac{a+b+c}{2}$$ plugging this in our formula we get after squaring and simplifying
$$- left( {a}^{6}-{a}^{4}{b}^{2}-{a}^{4}{c}^{2}-{a}^{2}{b}^{4}-6,{a}^{
2}{b}^{2}{c}^{2}+{b}^{6}-{b}^{4}{c}^{2} right) left( {a}^{2}+{b}^{2
}-{c}^{2} right)
=0$$
it remaines to show that the first factor can not be zero.
One idea: Using the formulas $$A=frac{1}{2}absin(gamma)$$ etc we get
$$frac{4A^2}{b^2c^2}+frac{4A^2}{a^2c^2}=frac{2A}{ab}$$ and using $$A=sqrt{s(s-a)(s-b)(s-c)}$$ where $$s=frac{a+b+c}{2}$$ plugging this in our formula we get after squaring and simplifying
$$- left( {a}^{6}-{a}^{4}{b}^{2}-{a}^{4}{c}^{2}-{a}^{2}{b}^{4}-6,{a}^{
2}{b}^{2}{c}^{2}+{b}^{6}-{b}^{4}{c}^{2} right) left( {a}^{2}+{b}^{2
}-{c}^{2} right)
=0$$
it remaines to show that the first factor can not be zero.
answered Dec 9 at 10:12
Dr. Sonnhard Graubner
73k42865
73k42865
add a comment |
add a comment |
If I read the second condition as
$$alpha-kbetaleq{piover2},quadbeta-kalphaleq{piover2}qquad forall >kin[-3,3] ,$$
and add these two inequalities in the case $k:=-3$ I obtain
$$4(alpha+beta)leq pi ,$$
or $alpha+betaleq{piover4}$. I don't see how a right triangle can be formed in this way, even without looking at the first condition. Note that in the linked source they are only talking about the case $k=3$.
1
$left | text{k} right |leqq 3$ is acceptable ! With $left | text{k} right |leqq 3$, for example: $text{A}= 4,text{B}+ frac{5,pi}{11},,text{C}= frac{6,pi}{11}- 5,text{B},,left | text{k} right |= 4Rightarrow text{B}neq frac{pi}{110} Rightarrow text{C}neq pi$ ! I understand your comment & I think $left | text{k} right |leqq 3$ is neccessary for my problem ! $text{k}= 3$ is my original problem, then I generalised it to $left | text{k} right |leqq 3$ , those are all of mine on Vietnamese Math Forum ( Diendantoanhoc.net ) ! Thanks for your interest !
– HaiDangel
Dec 10 at 1:19
1
There are some misunderstandings about my problem here: $lceil$ artofproblemsolving.com/community/c6h1725878p11175691 $rfloor$
– HaiDangel
Dec 10 at 1:29
add a comment |
If I read the second condition as
$$alpha-kbetaleq{piover2},quadbeta-kalphaleq{piover2}qquad forall >kin[-3,3] ,$$
and add these two inequalities in the case $k:=-3$ I obtain
$$4(alpha+beta)leq pi ,$$
or $alpha+betaleq{piover4}$. I don't see how a right triangle can be formed in this way, even without looking at the first condition. Note that in the linked source they are only talking about the case $k=3$.
1
$left | text{k} right |leqq 3$ is acceptable ! With $left | text{k} right |leqq 3$, for example: $text{A}= 4,text{B}+ frac{5,pi}{11},,text{C}= frac{6,pi}{11}- 5,text{B},,left | text{k} right |= 4Rightarrow text{B}neq frac{pi}{110} Rightarrow text{C}neq pi$ ! I understand your comment & I think $left | text{k} right |leqq 3$ is neccessary for my problem ! $text{k}= 3$ is my original problem, then I generalised it to $left | text{k} right |leqq 3$ , those are all of mine on Vietnamese Math Forum ( Diendantoanhoc.net ) ! Thanks for your interest !
– HaiDangel
Dec 10 at 1:19
1
There are some misunderstandings about my problem here: $lceil$ artofproblemsolving.com/community/c6h1725878p11175691 $rfloor$
– HaiDangel
Dec 10 at 1:29
add a comment |
If I read the second condition as
$$alpha-kbetaleq{piover2},quadbeta-kalphaleq{piover2}qquad forall >kin[-3,3] ,$$
and add these two inequalities in the case $k:=-3$ I obtain
$$4(alpha+beta)leq pi ,$$
or $alpha+betaleq{piover4}$. I don't see how a right triangle can be formed in this way, even without looking at the first condition. Note that in the linked source they are only talking about the case $k=3$.
If I read the second condition as
$$alpha-kbetaleq{piover2},quadbeta-kalphaleq{piover2}qquad forall >kin[-3,3] ,$$
and add these two inequalities in the case $k:=-3$ I obtain
$$4(alpha+beta)leq pi ,$$
or $alpha+betaleq{piover4}$. I don't see how a right triangle can be formed in this way, even without looking at the first condition. Note that in the linked source they are only talking about the case $k=3$.
answered Dec 9 at 12:00
Christian Blatter
172k7112325
172k7112325
1
$left | text{k} right |leqq 3$ is acceptable ! With $left | text{k} right |leqq 3$, for example: $text{A}= 4,text{B}+ frac{5,pi}{11},,text{C}= frac{6,pi}{11}- 5,text{B},,left | text{k} right |= 4Rightarrow text{B}neq frac{pi}{110} Rightarrow text{C}neq pi$ ! I understand your comment & I think $left | text{k} right |leqq 3$ is neccessary for my problem ! $text{k}= 3$ is my original problem, then I generalised it to $left | text{k} right |leqq 3$ , those are all of mine on Vietnamese Math Forum ( Diendantoanhoc.net ) ! Thanks for your interest !
– HaiDangel
Dec 10 at 1:19
1
There are some misunderstandings about my problem here: $lceil$ artofproblemsolving.com/community/c6h1725878p11175691 $rfloor$
– HaiDangel
Dec 10 at 1:29
add a comment |
1
$left | text{k} right |leqq 3$ is acceptable ! With $left | text{k} right |leqq 3$, for example: $text{A}= 4,text{B}+ frac{5,pi}{11},,text{C}= frac{6,pi}{11}- 5,text{B},,left | text{k} right |= 4Rightarrow text{B}neq frac{pi}{110} Rightarrow text{C}neq pi$ ! I understand your comment & I think $left | text{k} right |leqq 3$ is neccessary for my problem ! $text{k}= 3$ is my original problem, then I generalised it to $left | text{k} right |leqq 3$ , those are all of mine on Vietnamese Math Forum ( Diendantoanhoc.net ) ! Thanks for your interest !
– HaiDangel
Dec 10 at 1:19
1
There are some misunderstandings about my problem here: $lceil$ artofproblemsolving.com/community/c6h1725878p11175691 $rfloor$
– HaiDangel
Dec 10 at 1:29
1
1
$left | text{k} right |leqq 3$ is acceptable ! With $left | text{k} right |leqq 3$, for example: $text{A}= 4,text{B}+ frac{5,pi}{11},,text{C}= frac{6,pi}{11}- 5,text{B},,left | text{k} right |= 4Rightarrow text{B}neq frac{pi}{110} Rightarrow text{C}neq pi$ ! I understand your comment & I think $left | text{k} right |leqq 3$ is neccessary for my problem ! $text{k}= 3$ is my original problem, then I generalised it to $left | text{k} right |leqq 3$ , those are all of mine on Vietnamese Math Forum ( Diendantoanhoc.net ) ! Thanks for your interest !
– HaiDangel
Dec 10 at 1:19
$left | text{k} right |leqq 3$ is acceptable ! With $left | text{k} right |leqq 3$, for example: $text{A}= 4,text{B}+ frac{5,pi}{11},,text{C}= frac{6,pi}{11}- 5,text{B},,left | text{k} right |= 4Rightarrow text{B}neq frac{pi}{110} Rightarrow text{C}neq pi$ ! I understand your comment & I think $left | text{k} right |leqq 3$ is neccessary for my problem ! $text{k}= 3$ is my original problem, then I generalised it to $left | text{k} right |leqq 3$ , those are all of mine on Vietnamese Math Forum ( Diendantoanhoc.net ) ! Thanks for your interest !
– HaiDangel
Dec 10 at 1:19
1
1
There are some misunderstandings about my problem here: $lceil$ artofproblemsolving.com/community/c6h1725878p11175691 $rfloor$
– HaiDangel
Dec 10 at 1:29
There are some misunderstandings about my problem here: $lceil$ artofproblemsolving.com/community/c6h1725878p11175691 $rfloor$
– HaiDangel
Dec 10 at 1:29
add a comment |
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Do you mean "for all $k$ with $|k|leq3,$" or "for some $k$ with $|k|leq3,$"?
– Christian Blatter
Dec 9 at 11:01
1
I mean for all $text{k}$ ! Thanks !
– HaiDangel
Dec 9 at 12:33