Question

Find cosα given that sinα = 5/13 and α is in quadrant II

Answer 1

Answer:

cos α = - $\frac{12}{13}$

Step-by-step explanation:

Since α is in second quadrant then cosα < 0

Using the identity

sin²α + cos²α = 1 then

cosα = - $\sqrt{1-sin^2\alpha }$

         = - $\sqrt{1-(\frac{5}{13})^2 }$

         = - $\sqrt{1-\frac{25}{169} }$

         = - $\sqrt{\frac{144}{169} }$

         = - $\frac{12}{13}$