cos(π/4-a)=3/5,sin(π/4-a)=-4/5
sin(5π/4+b)=-12/13 =-sin(π/4+b)
12/13 =sin(π/4+b),cos(π/4+b)=5/13
sin(a+b)=sin[(π/4+b)-(π/4-a)](代换法)
=36/65+20/65=56/65
cos(π/4-a)=3/5,sin(π/4-a)=-4/5
sin(5π/4+b)=-12/13 =-sin(π/4+b)
12/13 =sin(π/4+b),cos(π/4+b)=5/13
sin(a+b)=sin[(π/4+b)-(π/4-a)](代换法)
=36/65+20/65=56/65