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 = $\frac{AB}{AC}$ = $\frac{3}{5}$.