已知a∈(π/4,3π/4),b∈(0,π/4),cos(π/4-a)=4/5,sin(3π/4,b)=5/13,求co
已知sin[a-b]cos a-cos[b-a]sin a=3/5,b是第三象限角,求sin[b+5π/4]的值
已知a∈(π/4,3π/4),b∈(0,π/4),cos(π/4-a)=4/5,sin(3π/4,b)=5/13,求co
已知sin(A+B)=4/5,sinA=3/5,A,B∈[0,π/2],(1)求cos(A+B)的值 (2)求cosB的
已知A B属于3π/4到π,SIN(A+B)=-3/5,SIN(B-π/4)=12/13,求COS(A+π/4
已知0<A<π/2<B<π,cos(B-π/4)=1/3,sin(A+B)=4/5求cos(a+
已知sin(a+2b)=4/5,cos(a+b)=12/13(a+2b,a+b)属于(0~2π)求sinb
已知向量a=(cosa,sina),b=(cosβ,sinβ),c=(-1,0).设a=π/4,且a⊥(b+c),求co
已知a,b∈(3π/4,π),sin(a+b)= - 3/5,sin(b-π/4)=12/13,求cos(a+π/4)
已知π/2<B<A<3π/4,cos(A-B)=12/13,sin(A+B)=-3/5,求sin2A
已知角ab sin(a+b)=-3/5 sin(b-π/4)=12/13 求cos(a+π/4)) 答案是-56/65
已知角ab sin(a+b)=-3/5 sin(b-π/4)=12/13 求cos(a+π/4))
已知a,b属于(3π/4,π),sin(a+b)=-3/5,sin(b-π/4)=12/13,则cos(a+4/π)=