1.(1-sint)(1+sint)=2.sin50/sin100=3.cos18-sin18/cos36=4.2sin165cos165=5.=

Формулы: cos 2а = 1 - sinа; cos 2а = cos а - sin а; sin 2а = 2sin а * cos а.
1. (1 - sin t)(1 + sin t) = 1 - sin t + sin t - sin t = 1 - sin t = cos 2t.
2. sin50/ sin100 = 1/2.
3. cos18 - sin18 / cos36 = cos36 / cos36 = 1.
4. 2sin165 cos165 = sin330 = - 1/2.