a) Rút gọn các biểu thức:

i) (x + 5)(x – 5) – (x2 – 1)

= x2 - 25 - x2 + 1

= -24

`Answer:`

`a)`

`A=5(x+1)^2-3(x-3)^2-4(x^2-4)`

`=>A=5(x^2+2x+1)-3(x^2-6x+9)-4x^2+16`

`=>A=5x^2+10x+5-3x^2+18x-27-4x^2+16`

`=>A=(5x^2-3x^2-4x^2)+(10x+18x)+(5-27+16)`

`=>A=-2x^2+28x-6`

`b)`

`B=5(x+1)^2-3(x-3)^2-4(x+2)(x-2)`

`=2x(3x+5)-3(3x+5)-2x(x^2-4x+4)-[(2x)^2-3^2]`

`=6x^2+10x-9x-15-2x^3+8x^2-8x-4x^2+9`

`=(6x^2-4x^2+8x^2)-2x^3+(10x-9x-8x)+(-15+9)`

Thay `x=-7` vào ta được:

`B=10(-7)^2-2(-7)^3-7(-7)-6`

`=>B=10.49-2(-343)+49-6`

`=>B=490+686+49-6`

`=>B=1219`

\(x\ge-\dfrac{4}{5}\)

\(A=5x+2+\left|5x+4\right|=5x+2+5x+4=10x+6\)

\(x< -\dfrac{4}{5}\)

\(A=5x+2+\left|5x+4\right|=5x+2-5x+4=6\)

\(\left(x-1\right)^3-x\left(x-2\right)\left(x+2\right)+3\left(x-5\right)^2\\ =x^3-3x^2+3x-1-x\left(x^2-4\right)+3\left(x^2-10x+25\right)\)

\(=x^3-3x^2+3x-1-x^3+4x+3x^2-30x+75\)

\(=74-23x\)

a. = \(\dfrac{2}{x+5}\)+\(\dfrac{2x+30}{\left(x-5\right)\left(x+5\right)}\)

= 2.(x-5) + 2x+30

= 2x-10+2x+30

=4x+20

b. x=9

4x+20

=4.9+20

=36+20

=56

đề bài lỗi bn ơi

Bạn nên gõ đề bằng công thức toán (biểu tượng $\sum$ góc trái khung soạn thảo) để mọi người hiểu đề và hỗ trợ bạn tốt hơn nhé.

\(a,M=\dfrac{\left(x-\sqrt{2}\right)^2}{\left(x-\sqrt{2}\right)\left(x+\sqrt{2}\right)}=\dfrac{x-\sqrt{2}}{x+\sqrt{2}}\\ b,N=\dfrac{x+\sqrt{5}}{\left(x+\sqrt{5}\right)^2}=\dfrac{1}{x+\sqrt{5}}\)

\(N=\dfrac{x+\sqrt{5}}{x^2+2x\sqrt{5}+5}=\dfrac{1}{x+\sqrt{5}}\)

a) ĐKXĐ: \(x\ne-3,x\ne2\)

b) \(A=\dfrac{\left(x-2\right)\left(x+2\right)-5-\left(x+3\right)}{\left(x+3\right)\left(x-2\right)}=\dfrac{x^2-x-12}{\left(x+3\right)\left(x-2\right)}=\dfrac{\left(x+3\right)\left(x-4\right)}{\left(x+3\right)\left(x-2\right)}=\dfrac{x-4}{x-2}\)

c) \(A=\dfrac{x-4}{x-2}=\dfrac{3-4}{3-2}=-1\)