Question

Consider the information given below
In $\triangle A B C, a=18, b=24$, and $c=30$.
The value of $\cos A$ is equal to

• A. $\frac{4}{5}$
• B. $\frac{3}{5}$
• C. 0
• D. 1

Answer 1

Answer: (A)

$a=18, b=24 a n d c=30$
$\therefore \cos A =\frac{b^2+c^2-a^2}{2 b c}=\frac{24^2+30^2-18^2}{2 \times 24 \times 30} $
$=\frac{576+900-324}{1440}=\frac{1152}{1440}=\frac{128}{160} $
$=\frac{8}{10}=\frac{4}{5}$