Attempt following question by selecting a choice to answer.
c
If
∠ A is in third quadrant and
cos A = - 513, then find the exact value of
cos A2.
e cA.
c -
31313B.
c-
526C.
c 21313D.
c -
21313
c
D
Step 1: cos A = - 513, 180° < ∠ A < 270°
Step 2: 90° < ∠A2 < 135°, therefore, A2 is a second-quadrant angle.
Step 3: cosA2 = - 1 + (-513)2[Using cosA2 = - 1 + cosA2.]
Step 4: cosA2 = - 826 = - 21313[Using cos A = - 513.]