5x²+7x-6=0(5x-3)(x+2)=0x=3/5或x=-2因为-1≤sina≤1所以：sina=3/5[sin(3π/2-a)tan(2π-a)]/[cos(π/2-a)cos(π/2+a)]=cosatana/(-sin²a)=-1/sina=-5/3很高兴为您解答,【华工王师】团队为您答题.请点击...