Ta có:[tex]S=\frac{1}{4}a+\frac{1}{a}+\frac{9}{4}b+\frac{4}{b}+\frac{3}{4}(a+b)\geq 2\sqrt{\frac{1}{4}a.\frac{1}{a}}+2\sqrt{\frac{9}{4}b.\frac{4}{b}}+\frac{3}{4}(a+b)\geq 1+6+\frac{9}{2}=\frac{23}{2}[/tex]
Dấu "=" xảy ra khi a = 2, b= 4
Ta có:[tex]S=\frac{1}{4}a+\frac{1}{a}+\frac{9}{4}b+\frac{4}{b}+\frac{3}{4}(a+b)\geq 2\sqrt{\frac{1}{4}a.\frac{1}{a}}+2\sqrt{\frac{9}{4}b.\frac{4}{b}}+\frac{3}{4}(a+b)\geq 1+6+\frac{9}{2}=\frac{23}{2}[/tex]
Dấu "=" xảy ra khi a = 2, b= 4