198․ա)cos(π/4-α)=(cosα+sinα)√2/2

բ)cos(π/4+α)=(cosα-sinα)√2/2

գ)sin(π/4-α)=(cos-sinα)√2/2

դ)sin(π/4+α)=(cosα+sinα)√2/2

199.ա)α=15º

√2(-√3-1)/4 , √2(-√3+1)/4 , 2-√3 , 2+√3

բ)α=75º

√2(-√3+1)/4 , √2(-√3-1)/4 , 2+√3 , 2-√3

201.ա)√2sin(π/4+α)-sinα = cosα

բ)√2cos(π/4-α)-cosα = sinα

202․ա)√2cos(3π/4+α)+cosα/√2cos(5π/4-α)+sinα=tgα

բ)sin(2π/3+α)+1/2sinα/sin7π/6-α+1/2cosα=ctgα

203․ա)sin27ºcos3º+cos27ºsin3º=sin(27+3)=1/2

բ)cos87ºcos27º+sin87ºsin27º=1/2

գ)cos92°cos28°-sin92°sin28°=-1/2

դ)sin105°cos45°-cos105°sin45°=√3/2

207․ա)tg(π/4+α) sinα=-3/√10 π<α<3/2 = -2

բ)ctg(3π/4-α) sinα=-5/√34 3π<α<2π=4