已知π/2
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已知π/2已知π/2已知π/2∵(secα)^2=1+(tanα)^2=1+(-3/4)^2=25/16∴secα=±5/4∵cosα=1/secα∴cosα=±4/5∵π/2∴cosα=-4/5则s
已知π/2
已知π/2
已知π/2
∵(secα)^2=1+(tanα)^2=1+(-3/4)^2=25/16
∴secα=±5/4
∵cosα=1/secα
∴cosα=±4/5
∵π/2<α<π
∴cosα=-4/5
则sinα=√[1-(cosα)^2]=3/5
sin(β-α)=±√1-[cos(β-α)]^2=±12/13
∵π/2<α<π,0<β<π/2
∴β-α<0
∴sin(β-α)=-12/13
sinβ=sin[(β-α)+α]=sin(β-α)cosα + cos(β-α)sinα =63/65