Відповіді АЛГЕБРА: 15.25

15.25

1) sin²80° – sin²40° = (sin80° – sin40°) • (sin80° + sin40°) =

= 2sin20° cos60° • 2sin60°cos20° = sin40° • 2 • 32 • 12 = 32sin40°.

2) cos²10° – cos²50° = (cos10° – cos50°) • (sin10° + cos50°) =

= –2sin30°sin(–20°) • 2cos30° cos(–20°) = sin60° • sin40° =

= 32sin40°.