Cho tam giác ABC có AB=c, BC=a, AC=b và \(P=\frac{a+b+c}{2}\)
CMR: a) (P-a)(P-b)(P-c) \(\le\)\(\frac{1}{8}abc\)
b) \(\frac{1}{P-a}+\frac{1}{P-b}+\frac{1}{P-c}\ge2\left(\frac{1}{a}+\frac{1}{b}+\frac{1}{c}\right)\)
c) \(\frac{1}{\left(P-a\right)^2}+\frac{1}{\left(P-b\right)^2}+\frac{1}{\left(P-c\right)^2}\ge\frac{P}{\left(P-a\right)\left(P-b\right)\left(P-c\right)}\)