Given $a=12 \mathrm{~cm}, b=9 \mathrm{~cm}$ and $c=15$, write ratio (in lowest terms) would represent cos A?
(remember to write a ratio as top/bottom)

Answer

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Answer

$\boxed{\cos A = 0}$

Steps

Step 1 ：$\cos A = \frac{a^2 + b^2 - c^2}{2ab}$

Step 2 ：$\cos A = \frac{12^2 + 9^2 - 15^2}{2 \cdot 12 \cdot 9}$

Step 3 ：$\cos A = \frac{144 + 81 - 225}{216}$

Step 4 ：$\cos A = \frac{0}{216}$

Step 5 ：$\boxed{\cos A = 0}$