Відповіді АЛГЕБРА: 15.37

15.37

1) 2cos80°cos50° + sin140° = 2 • 12(cos30° + cos130°) + sin140° =

= 32 + cos130° + sin140° = 32 + sin40° + sin140° = 32 + 2sin90° •

• cos50° = 32 + 2 • 1 • cos50° = 32 + 2cos50°.

2) 4cos40° – 1sin70° = 4cos40°sin70°-1sin70° = 4•cos40° cos20°-1sin70° =

= 4 • 12cos20°+cos60°- 1sin70° = 2cos20°+1-1sin70° = 2sin70°sin70° = 2.