\(a,ĐK:x\ne\pm2\\ b,A=\dfrac{5x+10+14x-28-20}{2\left(x-2\right)\left(x+2\right)}=\dfrac{19\left(x-2\right)}{2\left(x-2\right)\left(x+2\right)}=\dfrac{19}{2\left(x+2\right)}\\ c,x=-\dfrac{1}{2}\Leftrightarrow A=\dfrac{19}{2\left(2-\dfrac{1}{2}\right)}=\dfrac{19}{2\cdot\dfrac{3}{2}}=\dfrac{19}{3}\)

a)4².8²=32²

k giúp

`A=(-7sqrtx+6)/(x-4)+sqrtx/(sqrtx-2)`

`=(-7sqrtx+6)/(x-4)+(x+2sqrtx)/(x-4)`

`=(x+2sqrtx-7sqrtx+6)/(x-4)`

`=(x-5sqrtx+6)/(x-4)`

`=((sqrtx-2)(sqrtx-3))/((sqrtx-2)(sqrtx+2))`

`=(sqrtx-3)/(sqrtx+2)`

Rút gọn biểu thức
\(\left(8-5x\right)\left(x+2\right)+4\left(x-2\right)\left(x+1\right)+2\left(x-2\right)\left(x+2\right)+10\)
\(\Leftrightarrow8x+16-5x^2+10x+4\left(x^2+x-2x+2\right)+2\left(x^2+2x-2x+4\right)+10\)
\(\Leftrightarrow18x+26-5x^2+4\left(x^2-x+2\right)+2\left(x^2+4\right)\)
\(\Leftrightarrow18x-5x^2+26+4x^2-4x+8+2x^2+8\)
\(\Leftrightarrow18x-4x-5x^2+4x^2+2x^2+8+26+8\)
\(\Leftrightarrow14x+3x^2+42\)

4x+x^2

không biết

`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`