\(P=\left(a+\frac{1}{4a}\right)+\left(b+\frac{1}{4b}\right)+\frac{3}{4a}+\frac{35}{4b}\ge2\sqrt{a.\frac{1}{4a}}+2.\sqrt{b.\frac{1}{4b}}+\frac{3}{4.\frac{1}{2}}+\frac{35}{4.\frac{1}{2}}\)
\(P\ge\frac{2.1}{2}+\frac{2.1}{2}+\frac{3}{4.\frac{1}{2}}+\frac{35}{4.\frac{1}{2}}=21\)
P min =21 khi a=b =1/2