(-4,3)是角a终边上一点
得出
a是第二象限角
sina=3/5
cos(a-3π)=cos(a-3π+4π)=cos(a+π)=-cosa
tan(a-4π)=tana
sin(3π-a)=-sin(a-3π)=-sin(a-3π+4π)=-sin(a+π)=sina
cos(a+5π/2)=cos(a+5π/2-2π)=cos(a+π/2)=-sina
cos(a-3π)*tan(a-4π)/sin(3π-a)*cos(a+5π/2)
=[(-cosa)tana]/[sina*(-sina)]
=-sina/-sin²a
=1/sina
=5/3