Question

Find the value of cos θ if the angle θ is in the third quadrant and sinθ= -0.8

Answer 1

Correct option is D) -0.6.

Step-by-step explanation:

We have $sin\alpha = -0.8$ . Also, we know that $cos\alpha = \sqrt{1- (sin\alpha } )^{2}$ . Let's find out value of $cos\alpha$  using above formula:

$cos\alpha = \sqrt{1- (sin\alpha } )^{2}$

⇒ $cos\alpha = \sqrt{1- (sin\alpha } )^{2}$

⇒ $cos\alpha = \sqrt{1- (-0.8 } )^{2}$

⇒ $cos\alpha = \sqrt{1- (0.64 } )^{}$

⇒ $cos\alpha = \sqrt{0.36}$

⇒ $cos\alpha = 0.6$

But we know that cos$\alpha$ is negative in third quadrant , Therefore $cos\alpha = -0.6$.

Hence, correct option is D) -0.6.