Given $a = 12 cm, b = 9 cm$ 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

$\cos A = 0$

Steps

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

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 ： $\cos A = 0$