>>914

交点のx座標をα　→　sin2α=kcosα　→　sinα=k/2

1/2 * ∫[0,π/2]sin2x dx = ∫[α,π/2] (sin2x-kcosx) dx
1/2 = (1+cos2α)/2 -(k-sinα)　→　k^2-4k+2=0 →　k=2-√2