cos2α=3/5,α∈(-π/2,0)则sin4α=

问题描述:

cos2α=3/5,α∈(-π/2,0)则sin4α=

cos2α=3/5sin2α=-√1-(cos2α)^2=-√1-(3/5)^2=-4/5
sin4α=2sin2αcos2α=2×(-4/5)×3/5=-24/25