Question

[Lê Châu Linh]

cho 3 số thực dương ab,c thỏa mãn:ab+bc+ca=1. Chứng minh:((b+c)*căn(a^2+1)/(căn(b^2+1)*căn(c^2+1)

Answer 1

[Thắng Nguyễn]

Đặt \(THANG=\frac{\left(b+c\right)\sqrt{a^2+1}}{\sqrt{b^2+1}\sqrt{c^2+1}}\)

\(=\frac{\left(b+c\right)\sqrt{a^2+ab+bc+ca}}{\sqrt{b^2+ab+bc+ca}\sqrt{c^2+ab+bc+ca}}\)

\(=\frac{\left(b+c\right)\sqrt{\left(a+b\right)\left(a+c\right)}}{\sqrt{\left(b+c\right)\left(a+b\right)}\sqrt{\left(a+c\right)\left(b+c\right)}}\)

\(=\frac{\left(b+c\right)}{\sqrt{\left(b+c\right)}\sqrt{\left(b+c\right)}}=\frac{\left(b+c\right)}{\sqrt{\left(b+c\right)^2}}\)

\(=\frac{b+c}{b+c}=1\left(b,c\in R^+\right)\)

Answer 2

[Lê Châu Linh]

chứng minh bằng 1