sin^2\alpha*cos^2\alpha=1
a)
4sin^2\alpha+4cos^2\alpha-3=4(sin^2\alpha+cos^2\alpha)-3=4*1-3=1
b)
2cos^2\alpha-5+2sin^2\alpha-3=2sin^2\alpha+2cos^2\alpha-8=
=2(sin^2\alpha+cos^2\alpha)-8=2*1-8=-6
c)
3-sin^2\alpha-cos^2\alpha=3-(sin^2\alpha+cos^2\alpha)=3-1=2