Answer:
1/8
Step-by-step explanation:
sin²(π/8) − cos⁴(3π/8)
Use power reduction formulas:
1/2 (1 − cos(2×π/8)) − 1/8 (3 + 4 cos(2×3π/8) + cos(4×3π/8))
Simplify:
1/2 (1 − cos(π/4)) − 1/8 (3 + 4 cos(3π/4) + cos(3π/2))
1/2 (1 − √2/2) − 1/8 (3 + 4 (-√2/2) + 0)
1/2 − √2/4 − 1/8 (3 − 2√2)
1/2 − √2/4 − 3/8 +√2/4
1/2 − 3/8
1/8
