bài 1:
`a) a^3-a^2c+a^b-abc`
`=a(a^2-ac+ab-bc)`
`=a[a(a-c)+b(a-c)]`
`=a(a-c)(a+b)`
`b) (x^2+1)^2-4x^2`
`=(x^2+1)^2-(2x)^2`
`=(x^2-2x+1)(x^2+2x+1)`
`=(x-1)^2(x+1)^2`
`c) x^2-10x-9y^2+25`
`=(x^2-10x+25)-9y^2`
`=(x-5)^2-(3y)^2`
`=(x-3y-5)(x+3y-5)`
`d) 4x^2-36x+56`
`=4(x^2-9x+14)`
`=4(x^2-7x-2x+14)`
`=4[x(x-7)-2(x-7)]`
`=4(x-7)(x-2)`
bài 2:
`a) (3x+4)^2-(3x-1)(3x+1)=49`
`<=> 9x^2+24x+16-9x^2+1-49=0`
`<=> 24x-32=0`
`<=> 3x-4=0`
`<=> x=4/3`
`b) x^2-4x+4=9(x-2)`
`<=>(x-2)^2-9(x-2)=0`
`<=> (x-2)(x-2-9)=0`
`<=> (x-2)(x-11)=0`
`<=>`\(\left[ \begin{array}{l}x-2=0\\x-11=0\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}x=2\\x=11\end{array} \right.\)
`c) x^2-25=3x-15`
`<=> (x-5)(x+5)-3(x-5)=0`
`<=> (x-5)(x+5-3)=0`
`<=> (x-5)(x+2)=0`
`<=>`\(\left[ \begin{array}{l}x-5=0\\x+2=0\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}x=5\\x=-2\end{array} \right.\)
`d) (x-1)^3+3(x+1)^2=(x^2-2x+4)(x+2)`
`<=> x^3-3x^2+3x-1+3(x^2+2x+1)=x^3+8`
`<=> x^3-3x^2+3x-1+3x^2+6x+3-x^3-8=0`
`<=> 9x-6=0`
`<=> 3x-2=0`
`<=> x=2/3`
