Question

Consider the information given below
In $△ABC,a=18,b=24$, 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)

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