ta có :            \(\frac{a^3-4a^2-a+4}{a^3-7a^2+14a-8}\)

          =          \(\frac{\left(a-1\right)\left(a+1\right)\left(a-4\right)}{\left(a-4\right)\left(a-2\right)\left(a-1\right)}\)

          =           \(\frac{a+1}{a-2}\)

          nhớ nha

a/ (x+y)³-(x-y)³-2y³

= (x³+3x²y+3xy²+y³)-(x³-3x²y+3xy²-y³)-2y³

= x³+3x²y+3xy²+y³-x³+3x²y-3xy²+y³-2y³

= 6xy²

b/ (x+2)(x²-2x+4)-(16-x³)

= x³-2x²+4x+2x²-4x+8-16+x³

= 2x³-8

c/ (2a+b)(4a²-2ab+b²)-(2a-b)(4a²+2ab+b²)

= (8a³+b³)-(8a³-b³)

= 8a³+b³-8a³+b³

= 2b³

a: ĐKXĐ: a∉{-1/3;-3}

\(\frac{3a-1}{3a+1}+\frac{a-3}{a+3}=2\)

=>\(\frac{\left(3a-1\right)\left(a+3\right)+\left(3a+1\right)\left(a-3\right)}{\left(3a+1\right)\left(a+3\right)}=2\)

=>\(2\left(3a+1\right)\left(a+3\right)=\left(3a-1\right)\left(a+3\right)+\left(3a+1\right)\left(a-3\right)\)

=>\(2\left(3a^2+9a+a+3\right)=3a^2+9a-a-3+3a^2-9a+a-3\)

=>\(6a^2+20a+6=6a^2-6\)

=>20a=-12

=>a=-3/5(nhận)

b: ĐKXĐ: a∉{5/2;2/3}

\(\frac{2a-9}{2a-5}+\frac{3a}{3a-2}=2\)

=>\(\frac{2a-5-4}{2a-5}+\frac{3a-2+2}{3a-2}=2\)

=>\(1-\frac{4}{2a-5}+1+\frac{2}{3a-2}=2\)

=>\(\frac{2}{3a-2}=\frac{4}{2a-5}\)

=>\(\frac{4}{6a-4}=\frac{4}{2a-5}\)

=>6a-4=2a-5

=>4a=-1

=>a=-1/4(nhận)

c: ĐKXĐ: a<>-3

\(\frac{10}{3}-\frac{3a-1}{4a+12}-\frac{7a+2}{6a+18}=2\)

=>\(\frac{3a-1}{4a+12}+\frac{7a+2}{6a+18}=\frac{10}{3}-2=\frac43\)

=>\(\frac{3\left(3a-1\right)}{12\left(a+3\right)}+\frac{2\left(7a+2\right)}{12\left(a+3\right)}=\frac43\)

=>\(\frac{9a-3+14a+4}{12\left(a+3\right)}=\frac{4\cdot4\cdot\left(a+3\right)}{12\left(a+3\right)}\)

=>23a+1=16(a+3)=16a+48

=>7a=47

=>a=47/7(nhận)

Sửa lại đề bài:  1 / 2a- b 

                   ( MÁY MK KO ĐÁNH ĐC PHÂN SỐ MONG BN THÔNG CẢM)

mới lm đc nhé bn! 

a) ĐKXĐ: bn tự lm nhé ! 

bn biến đổi: 2a³-b+2a-a²b =  (2a-b)  + ( 2a³-a²b) = (2a-b) + a²(2a-b) = (2a-b)(a²+1) 

rồi bn nhân 1 / 2a+b với a²+1 rồi trừ 2 phân thức với nhau sẽ ra 0 => A=0

Bạn nào giúp tớ với!

`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`

\(4a^2+b^2=5ab\)

\(\Rightarrow4a^2-5ab+b^2=0\)

\(\Rightarrow\left(4a^2-4ab\right)-\left(ab-b^2\right)=0\)

\(\Rightarrow4a\left(a-b\right)-b\left(a-b\right)=0\)

\(\Rightarrow\left(a-b\right)\left(4a-b\right)=0\)

Làm nốt