A.
B.
C.
D.
Step 1: sin B =
45, 90° <
∠
B < 180°

Step 2: cos B = -
35[Cosine is negative in quadrant II.]
Step 3: 45° <
∠B2 < 90°, therefore,
∠B2 is a first-quadrant angle.
Step 4: cos
B2 = +
1 + cosB2[ Formula for half-angle .]
Step 5: =
1+(- 3)52 =
15 =
55[cos B = -
35.]