Question

已知tanα=-3/4,α在第二象限,求cos2α+sin2α

Answer 1

secα=-√（1+9/16)=-5/4,

cosα=-4/5,

sinα=3/5,

sin2α=2*(-4/5)*(3/5)=-24/25,

cos2α=1-2(sinα)^2=1-18/25=7/25,

cos2α+sin2α=-17/25.