cos(a-π/6)+sina=4√3/5cosa*cos(π/6)+sina*sin(π/6)+sina=4√3/5(√3/2)*cosa+(3/2)*sina=4√3/5√3*sin(a+π/6)=4√3/5所以sin(a+π/6)=4/5故sin(a+7π/6)=sin(a+π/6+π)=-sin(a+π/6)=-4/5如果不懂,请Hi我,祝...