Question

Найти множество значений функции:
y = 10 - 8*cos²9x * sin²9x.

Answer 1

$y=10-8\, cos^2x\cdot sin^29x\\\\y=10-2\cdot (2\, sin9x\cdot cos9x)^2=10-2\cdot sin^218x=2\cdot (5-sin^218x)\\\\0\leq sin^218x\leq 1\\\\-1\leq (-sin^218x)\leq 0\\\\5-1\leq (5-sin^218x)\leq 5+0\\\\4\leq (5-sin^218x)\leq 5\\\\8\leq 2\cdot (5-sin^218x)\leq 10\\\\y\in [\, 8,10\, ]$