Bài 1 :
Cho x, y, z \(\ne0\) ; A = \(\dfrac{y}{z}+\dfrac{z}{y}\) ; B = \(\dfrac{z}{x}+\dfrac{x}{z}\) ; C = \(\dfrac{x}{y}+\dfrac{y}{x}\)
Tính A\(^2\) + B\(^2\) + C\(^2\) - ABC
Bài 2 :
Cho x = \(\dfrac{a}{b+c}\) ; y = \(\dfrac{b}{c+a}\) ; z = \(\dfrac{c}{a+b}\)
Tính xy + yz + xz + 2xyz
Bài 3: Rút gọn
\(A=\left(1+\dfrac{b^2+c^2-a^2}{2abc}\right)\times\dfrac{1+\dfrac{a}{b+c}}{1-\dfrac{a}{b+c}}\times\dfrac{b^2+c^2-\left(b-c\right)^2}{a+b+c}\)