紧急求助数学问题!希望4月15号得到答案
解:(1) ∵α∈(π/4,3π/4), ∴ -π/2<π/4-α<0
cos(α-π/4)=cos(π/4-α)=3/5
sin(π/4-α)=-4/5 sin(α-π/4)=-sin(π/4-α)=4/5
∵β∈(0,π/4), ∴5π/4<5π/4+β<3π/2
sin(5π/4+β)=-12/13
cos(β+5π/4)=-5/13
∴cos(α+β)=-cos(π+α+β)
=-cos(α-π/4+β+5π/4)
=-[ cos(α-π/4)×cos(β+5π/4)-sin(α-π/4)×sin(5π/4+β)]
=-[(3/5)×(-5/13)-(4/5)×(-12/13)]
...全部
解:(1) ∵α∈(π/4,3π/4), ∴ -π/2<π/4-α<0
cos(α-π/4)=cos(π/4-α)=3/5
sin(π/4-α)=-4/5 sin(α-π/4)=-sin(π/4-α)=4/5
∵β∈(0,π/4), ∴5π/4<5π/4+β<3π/2
sin(5π/4+β)=-12/13
cos(β+5π/4)=-5/13
∴cos(α+β)=-cos(π+α+β)
=-cos(α-π/4+β+5π/4)
=-[ cos(α-π/4)×cos(β+5π/4)-sin(α-π/4)×sin(5π/4+β)]
=-[(3/5)×(-5/13)-(4/5)×(-12/13)]
=-33/65。
(2)由sin(5π/4+β)= -12/13
得sin(π/4+β)= 12/13。
∴sin(α+β)=sin[(π/4+β)-(π/4-α)]
=sin(π/4+β)cos(π/4-α)]-cos(π/4+β)sin(π/4-α)
=12/13×3/5-(-5/13)×4/5
=56/65;
则:tan(α+β)=sin(α+β)/cos(α+β)=(56/65)/(-33/65)=-56/33
。收起