b1:cmr:từ đẳng thức $\frac{a^2(x-b)(x-c)}{(a-b)(a-c)}+\frac{b^2(x-c)(x-a)}{(b-c)(b-a)}+\frac{c^2(x-a)(x-b)}{(c-a)(c-b)}$
$=x$
b2:
c/m từ$\frac{1}{a}+\frac{1}{b}+\frac{1}{c}=\frac{1}{a+b+c} \Rightarrow \frac{1}{a^n}+\frac{1}{b^n}+\frac{1}{c^n}$$=\frac{1}{a^n+b^n+c^n}$ với n lẻ
b3:c/m:nếu $a+b+c=0 \Rightarrow (\frac{a-b}{c}+\frac{b-c}{a}+\frac{c-a}{b})(\frac{c}{a-b}+\frac{a}{b-c}+\frac{b}{c-a})$$=9$
b4:c/m: từ $(y-z)^2+(z-x)^2+(x-y)^2=(y+z-2x)^2+(z+x-2y)^2+(x+y-2z)^2$
b5: giả sử $x=\frac{a-b}{a+b};y=\frac{b-c}{b+c};z=\frac{c-a}{c+a}$ $c/m:(1+x)(1+y)(1+z)=(1-x)(1-y)(1-z)$
b6:cho $x+y+z=0 ;x,y,z\neq0$rút gọn$:A=\frac{x^2}{x^2-y^2-z^2}+\frac{y^2}{y^2-z^2-x^2}+\frac{z^2}{z^2-x^2-y^2}$