sin和cos周期都是2π 所以sin(a-3π)=sin(a+π)=-sina 2cos(a-4π)=2cosa 所以sina=-2cosa [sin(π-a)+5cos((3π/2)-a)]/[2sin(3π/2+a)-sin(-a)] =[sina+5cos(π+(π/2)-a)]/[2sin(π+π/2+a)+sina] =[sina-5cos((...