Giải thích các bước giải:
Bài 3:
$1.1+x^2=xy+yz+zx+x^2=y(x+z)+x(x+z)=(x+y)(x+z)$
$2.1+y^2=(y+x)(y+z)$
$1+z^2=(z+x)(z+y)$
$\rightarrow x.\sqrt{\dfrac{(1+y^2)(1+z^2)}{1+x^2}}=x\sqrt{\dfrac{(y+x)(y+z)(z+x)(z+y)}{(x+y)(x+z)}}=x(y+z)$
Tương tự
$\rightarrow P=x(y+z)+y(x+z)+z(x+y)=2(xy+yz+zx)=2$