已知α,β属于四分之三π,π,sin(α+β)=-五分之三,sin(β-四分之π)=十三分之十二,则cos(α+四分之π)

你好!数学之美团为你解答α,β∈(3π/4,π)α+β∈(3π/2,2π),β - π/4 ∈(π/2,3π/4)sin(α+β) = - 3/5,sin(β - π/4) = 12/13∴cos(α+β) = 4/5,cos(β - π/4) = - 5/13cos(α+π/4) = cos [ (α+β) - (β...