[tex]a) \\sin36*cos54+cos36*sin54-\frac12=\\sin36*cos(90-36)+cos36*sin(90-36)-\frac12=\\sin36*sin36+cos36*cos36-\frac12=\\sin^236+cos^236-\frac12=1-\frac12=\frac12[/tex]
[tex](1-cos20)(1+cos20)-cos^270+2tg75*tg15=\\1-cos^220-cos^270+2tg75*ctg75=\\sin^220-cos^2(90-20)+2*\frac{sin75}{cos75}*\frac{cos75}{sin75}=\\sin^220-sin^220+2*1=\\0+2=2[/tex]
