$VT=\frac{2}{\sqrt{3}}(cos\frac{A}{2}.\frac{\sqrt{3}}{2}+cos\frac{B}{2}.\frac{\sqrt{3}}{2})+\sqrt{3}(\frac{cos\frac{A}{2}}{\sqrt{3}}.sin\frac{B}{2}+\frac{cos\frac{B}{2}}{\sqrt{3}}.sin\frac{A}{2})\leq \frac{1}{\sqrt{3}}((cos^2\frac{A}{2}+3/4)+(cos^2B/2+3/4))+\frac{\sqrt{3}}{2}((\frac{cos^2\frac{A}{2}}{3}+sin^2B/2)+(cos^2B/2//3+sin^2A/2))=\frac{3\sqrt{3}}{2}$suy ra đpcmgõ muốn rời tay lun!
$VT=\frac{2}{\sqrt{3}}(cos\frac{A}{2}.\frac{\sqrt{3}}{2}+cos\frac{B}{2}.\frac{\sqrt{3}}{2})+\sqrt{3}(\frac{cos\frac{A}{2}}{\sqrt{3}}.sin\frac{B}{2}+\frac{cos\frac{B}{2}}{\sqrt{3}}.sin\frac{A}{2})\leq \frac{1}{\sqrt{3}}((cos^2\frac{A}{2}+3/4)+(cos^2B/2+3/4))+\frac{\sqrt{3}}{2}((\frac{cos^2\frac{A}{2}}{3}+sin^2B/2)+(cos^2B/2//3+sin^2A/2))=\frac{3\sqrt{3}}{2}$suy ra đpcmgõ muốn rời tay lun! hậu tạ cho mình nhé! hihi
$VT=\frac{2}{\sqrt{3}}(cos\frac{A}{2}.\frac{\sqrt{3}}{2}+cos\frac{B}{2}.\frac{\sqrt{3}}{2})+\sqrt{3}(\frac{cos\frac{A}{2}}{\sqrt{3}}.sin\frac{B}{2}+\frac{cos\frac{B}{2}}{\sqrt{3}}.sin\frac{A}{2})\leq \frac{1}{\sqrt{3}}((cos^2\frac{A}{2}+3/4)+(cos^2B/2+3/4))+\frac{\sqrt{3}}{2}((\frac{cos^2\frac{A}{2}}{3}+sin^2B/2)+(cos^2B/2//3+sin^2A/2))=\frac{3\sqrt{3}}{2}$suy ra đpcmgõ muốn rời tay lun!