18.19题,
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18.19题,18.19题, 18.19题,185sinαcosβ-5cosαsinβ=3sinαcosβ+3cosαsinβ2sinαcosβ=8cosαsinβsinαcosβ=4cos
18.19题,
18.19题,
18.19题,
18
5sinαcosβ-5cosαsinβ=3sinαcosβ+3cosαsinβ
2sinαcosβ=8cosαsinβ
sinαcosβ=4cosαsinβ
tanα=4tanβ
x=4
19
cos(π/2+α)= - 3/5
sin(π/2+α)= -4/5
sin2a= - sin(π+2α)= - 2sin(π/2+α)cos(π/2+α)= - 24/25
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