已知sinα=5/13,且a∈(π/2,π),求cos2α,sin2α及sinα/2的值

问题描述:

已知sinα=5/13,且a∈(π/2,π),求cos2α,sin2α及sinα/2的值

sinα=5/13,且a∈(π/2,π)cosα=-12/13cos2α=1-2sin^2α=1-2*(5/13)^2=1-50/169=119/169 sin2α=2sinαcosα=-120/169 cosα=1-2sin^2α/2=-12/13sin^2α/2=25/26 sinα=5/13,且a∈(π/2,π)s...