a: \(\sqrt{252}+\dfrac{1}{3}\sqrt{63}-\sqrt{175}\)

\(=4\sqrt{7}+\sqrt{7}-5\sqrt{7}\)

=0

BÀI 3:

bài 4:

Là mấy bài này em làm được bài nào chưa?

Chọn A

\(\left(a-\dfrac{a^2+b^2}{a+b}\right)\left(\dfrac{1}{b}+\dfrac{2}{a-b}\right)\)

\(=\dfrac{a^2+ab-a^2-b^2}{a+b}\cdot\dfrac{a-b+2b}{b\left(a-b\right)}\)

\(=\dfrac{b\left(a-b\right)}{a+b}\cdot\dfrac{a+b}{b\left(a-b\right)}\)

=1

\(\left(a-\dfrac{x^2+a^2}{x+a}\right)\left(\dfrac{2a}{x}-\dfrac{4a}{x-a}\right)\)

\(=\dfrac{ax+a^2-x^2-a^2}{x+a}\cdot\dfrac{2ax-2a^2-4ax}{x\left(x-a\right)}\)

\(=\dfrac{a\left(x-a\right)}{x+a}\cdot\dfrac{-2a^2-2ax}{x\left(x-a\right)}\)

\(=\dfrac{a}{x+a}\cdot\dfrac{-2a\left(a+x\right)}{x}\)

\(=\dfrac{-2a^2}{x}\)

\(\left(a-\dfrac{x^2+a^2}{x+a}\right)\left(\dfrac{2a}{x}-\dfrac{4a}{x-a}\right)\)

\(=\dfrac{ax+a^2-x^2-a^2}{x+a}.\dfrac{2a\left(x-a\right)-4ax}{x\left(x-a\right)}\)

\(=\dfrac{x\left(a-x\right)}{x+a}.\dfrac{-2a^2-2ax}{x\left(x-a\right)}\)

\(=\dfrac{x\left(a-x\right)}{x+a}.\dfrac{-2a\left(a+x\right)}{x\left(x-a\right)}\)

\(=2a\)

11)11) 3x(x-5)²-(x+2)³+2(x-1)³-(2x+1)(4x²-2x+1)=3x(x²-10x+25)-(x³+6x²+12x+8)+2(x³-3x²+3x-1)-(8x³+1)=3x³-30x²+75x-x³-6x²-12x-8+2x³-6x²+6x-2-8x³-1=-4x³-42x²+63x-11

nhìn khó thế

Chọn A

A

A

các pro giúp em vớiiiiiiiiii ;-;