( x + 2 )( x² - 2x + x² ) - x( x - 5 )( x + 5 ) + 17

= ( x + 2 )( 2x² - 2x ) - x( x² - 25 ) + 17

= x( 2x² - 2x ) + 2( 2x² - 2x ) - x³ + 25x + 17

= 2x³ - 2x² + 4x² - 4x - x³ + 25x + 17

= x³ + 2x² + 21x + 17

Thế x = -1 ta được :

(-1)³ + 2.(-1)² + 2.(-21) + 17 = -1 + 2 - 21 + 17 = -3

nhầm dòng tính :v

(-1)³ + 2.(-1)² + 21.(-1) + 17 nhé .-.

Viết thế này có thể hiểu được ko bạn?

\(\left(3x^2-6x\right):3x-\frac{\left(1-3x\right)\left(1-3x\right)}{1-3x}\)

\(=\frac{3xx}{3x}-\frac{2\cdot3x}{3x}-\left(1-3x\right)\)

\(=x-2-1+3x\)

\(=4x-3\)

b) =(y^2-9)(y^2+9)-(y^4-4)

=y^4-81-y^4+4=-77

\(P=\frac{x+2}{\sqrt{x}^3-1}+\frac{\sqrt{x}+1}{x+\sqrt{x}+1}-\frac{\sqrt{x}+1}{\left(\sqrt{x}-1\right)\left(\sqrt{x}+1\right)}\)

\(P=\frac{x+2}{\left(\sqrt{x}-1\right)\left(x+\sqrt{x}+1\right)}+\frac{\sqrt{x}+1}{x+\sqrt{x}+1}-\frac{1}{\sqrt{x}-1}\)

\(P=\frac{x+2+x-1-x-\sqrt{x}-1}{\left(\sqrt{x}-1\right)\left(x+\sqrt{x}+1\right)}\)

2,

\(A=\frac{5\left(\sqrt{7}-\sqrt{2}\right)}{\left(\sqrt{7}-\sqrt{2}\right)\left(\sqrt{7}+\sqrt{2}\right)}+\frac{\sqrt{2}+1}{\left(\sqrt{2}-1\right)\left(\sqrt{2}+1\right)}-\frac{7\sqrt{7}}{7}\)

\(A=\frac{5\left(\sqrt{7}-\sqrt{2}\right)}{7-2}+\frac{\left(\sqrt{2}+1\right)}{2-1}-\sqrt{7}\)

\(A=\sqrt{7}-\sqrt{2}+\sqrt{2}+1-\sqrt{7}=1\)

\(P=\frac{\sqrt{x}\left(\sqrt{x}-1\right)}{\left(\sqrt{x}-1\right)\left(x+\sqrt{x}+1\right)}=\frac{\sqrt{x}}{x+\sqrt{x}+1}\)

a) \(x.\left(x+4\right)\left(x-4\right)-\left(x^2+1\right)\left(x^2-1\right)=x.\left(x^2-16\right)-\left(x^4-1\right)=x^3-16x-x^4+1\)

ý này ko rút gọn được hết đâu.

b) \(\left(y-3\right)\left(y+3\right)\left(y^2+9\right)-\left(y^2+2\right)\left(y^2-2\right)=\left(y^2-9\right)\left(y^2+9\right)-\left(y^4-4\right)\)

\(=y^4-81-y^4+4=-77\)

c)  \(\left(a+b-c\right)^2-\left(a-c\right)^2-2ab+2bc=a^2+b^2+c^2+2ab-2bc-2ac-a^2+2ac-c^2-2ab+2bc=b^2\)

Trần Anh: Cảm ơn pạn nhiều nhé ~~!! ;) ;) ;) 

\(\left(9x-1\right)^2-2\left(9x-1\right)\left(5x-1\right)+\left(5x-1\right)^2=\left(9x-1-5x+1\right)^2=\left(14x\right)^2=196x^2\)

\(5^4.3^4-\left(15^4-1\right)=15^4-15^4+1=1\)

hay dong nao di nao

ngu thì câm

a, ĐKXĐ: \(x\ne\pm2\)

b, \(A=\frac{x^2}{x^2-4}-\frac{x}{x-2}+\frac{2}{x+2}\)

      \(=\frac{x^2-x\left(x+2\right)+2\left(x-2\right)}{\left(x-2\right)\left(x+2\right)}\)

      \(=\frac{x^2-x^2-2x+2x-4}{\left(x-2\right)\left(x+2\right)}\)

      \(=\frac{-4}{x^2-4}\)

c, Tại x = 1 ( t/m ĐKXĐ)

thì \(A=\frac{-4}{1^2-4}=\frac{4}{3}\)

làm tính nhân

(2x+1)(x-1)

làm tính chia

(3xy^2+6x^2y-9xy):3xy

các bạn giải giúp mình!!!