Problem: If the area of △ A B C \triangle \mathrm{ABC}△ A B C is 64 646 4 square inches and the geometric mean (mean proportional) between sides A B ABA B and A C ACA C is 12 121 2 inches, then sin A \sin \mathrm{A}sin A is equal to
Answer Choices:
A. 3 2 \dfrac{\sqrt{3}}{2}2 3
B. 3 5 \dfrac{3}{5}5 3
C. 4 5 \dfrac{4}{5}5 4
D. 8 9 \dfrac{8}{9}9 8
E. 15 17 \dfrac{15}{17}1 7 1 5
Solution:
The area of △ A B C \triangle A B C△ A B C (See figure) is 64 = 1 2 A B ⋅ A C sin A 64=\frac{1}{2} A B \cdot A C \sin A6 4 = 2 1 A B ⋅ A C sin A .
Now A B ⋅ A C = 144 A B \cdot A C=144A B ⋅ A C = 1 4 4 . Hence sin A = 2 × 64 144 = 8 9 \sin A=\frac{2 \times 64}{144}=\frac{8}{9}sin A = 1 4 4 2 × 6 4 = 9 8 .
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