Question

In a right angled triangle, as shown below, if AB = 3 cm, BC = 4 cm then what is the value of cos A?

• A. 3/5
• B. 4/5
• C. 3/4
• D. 2/3

Answer 1

The correct option is A

3/5

Since ABC is a right angled triangle, we can apply Pythagoras theorem to get the length of side AC (hypotenuse).
Therefore,$A{C}^2=A{B}^2+B{C}^2$
$\Rightarrow A{C}^2=3^2+4^2$
$\Rightarrow A{C}^2$ = 9 + 16 = 25
$\Rightarrow$ AC = $\sqrt{2}5$ = 5
$\Rightarrow$ AC = 5
Now, cos A = $\frac{AB}{AC}$ = $\frac{3}{5}$.