The sides of an acute triangle measure 17 cm, 16 cm, and 15 cm, respectively. The measure of the smallest angle of the triangle is a solution for A to which of the following equations?

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It is appropriate to use law of cosines.

$$ c^2=a^2+b^2-2ab\cos{C} $$

We are looking for the smallest angle of the triangle, which should be opposite the smallest side. Therefore,

$$ c=15, a=16, b=17 $$ $$ (15)^2=(16)^2+(17)^2-2(16)(17)\cos{A} $$ $$ \boxed{15^2 = 16^2+17^2-2(16)(17)\cos{A} } $$