sin[A-(2n+1)π/2]=sin(A-nπ-π/2)=-cos(A-nπ)
当n=2k+1时,原式=coaA=3/5
sinA=4/5
tanA+coA=4/3+3/4=25/12
当n=2k时,原式=-coaA=3/5,cosA=-3/5
sinA=4/5
tanA+coA=-4/3-3/4=-25/12
sin[A-(2n+1)π/2]=sin(A-nπ-π/2)=-cos(A-nπ)
当n=2k+1时,原式=coaA=3/5
sinA=4/5
tanA+coA=4/3+3/4=25/12
当n=2k时,原式=-coaA=3/5,cosA=-3/5
sinA=4/5
tanA+coA=-4/3-3/4=-25/12