Sin(-x)=-sinx , sin2x=2sinxcosx , sin²x+cos²x=1
((1-4sin²αcos²α)/(sinα+cosα)²)-2cosαsin(-α)=1
((1-2sinαcosα.2sinαcosα)/(sin²α+2sinαcosα+cos²α))+2cosαsinα=1
((1-sin2αsin2α)/(1+sin2α))+sin2α=1
(1-sin²2α)/(1+sin2α)=1-sin2α
(1+sin2α)(1-sin2α)/(1+sin2α)=1-sin2α
1-sin2α=1-sin2α
( 1+sin2α≠0, sin2α≠-1, 2α≠-π/2+2kπ, α≠-π/4+kπ, k∈Z)
1) 150:3=50
2) через 5 часов
3) 8-5=3. 300:3=100
4) 300+300=600:8=75