Changing the side of a triangle without changing area?
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$triangle ABC$ has vertices $A=(8,2)$, $B=(0,6)$ and $C=(-3,2)$. Point $C$ can be moved along a certain line with points $A$ and $B$ remaining stationary so that the area of $ABC$ will not change? What is the slope of that line? The answer is $-frac12$, but I don't understand why or even how to come to this conclusion. Working backwards, I see that $-frac12$ is also the slope of line $AB$, but I don't know why this information is related or how to solve another problem of this type but not the exact same.
analytic-geometry triangle area slope
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edited Apr 17 '16 at 5:44