Question

If sin A = 3/5, what is the value of cos A?

• A. 4/5
• B. 4/9
• C. 2/5
• D. 1/5

Answer 1

The correct option is A 4/5

We know that,
$si{n}^{2}A+co{s}^{2}A=1\Rightarrow \cos A=\sqrt{1-{\sin }^{2}A}\Rightarrow \cos A=\sqrt{1-(\frac{3}{5}{)}^2}\Rightarrow \cos A=\sqrt{1-\frac{9}{25}}\Rightarrow \cos A=\sqrt{\frac{25-9}{25}}\Rightarrow \cos A=\sqrt{\frac{16}{25}}\Rightarrow \cos A=\frac{4}{5}$