A)2sint/2cost/2/2cos²t/2=sint/2/cost/2=tgt/2
б)(cos²t/2-sin²t/2)/(cost/2+sint/2)=(cost/2-sint/2)(cost/2+sint/2)/(cost/2+sint/2)=cost/2-sint/2
в)2sin2tcos2t/cos2t=2sin2t
г)(cos2t-sin2t)/(cos²2t-sin²2t)=(cos2t-sin2t)/(cos2t-sin2t)(cos2t+sin2t)=1/(cos2t+sin2t)