π/4
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π/4π/4π/4sin(α+β)=-sin[π+(α+β)]=-sin(π/4+α+3π/4+β)=-[sin(π/4+α)cos(3π/4+β)+cos(π/4+α)sin(3π/4+β)]=-[
π/4
π/4
π/4
sin(α+β)=-sin[π+(α+β)]=-sin(π/4+α+3π/4+β)=-[sin(π/4+α)cos(3π/4+β)+ cos(π/4+α)sin(3π/4+β)]=-[4/5*-12/13+ -3/5*5/13]=63/65