Đáp án:
`a)x=-5`
`b)x=3/2`
`c)x=14`
`d)x=8`
`e)x=5/2`
`f)x=1`
Giải thích các bước giải:
`a)3(x+2)^2+(2x-1)^2-7(x-3)(x+3)=36`
`⇔3(x²+4x+4)+4x²-4x+1-7(x²-9)=36`
`⇔3x²+12x+12+4x²-4x+1-7x²+63=36`
`⇔(3x²+4x²-7x²)+(12x-4x)+(12+1+63)=36`
`⇔8x+76=36`
`⇔8x=36-76`
`⇔8x=-40`
`⇔x=(-40):8`
`⇔x=-5`
Vậy `x=-5`
`b)(x-1)(x²+x+1)-x(x+2)(x-2)=5`
`⇔x³-1-x(x²-4)=5`
`⇔x³-1-x³+4x=5`
`⇔(x³-x³)+4x-1=5`
`⇔4x-1=5`
`⇔4x=5+1`
`⇔4x=6`
`⇔x=6/4`
`⇔x=3/2`
Vậy `x=3/2`
`c)(x-1)³-(x+3)(x²-3x+9)+3(x²-4)=2`
`⇔x³-3x²+3x-1-(x³+27)+3x²-12=2`
`⇔x³-3x²+3x-1-x³-27+3x²-12=2`
`⇔(x³-x³)+(-3x²+3x²)+3x-(1+27+12)=2`
`⇔3x-40=2`
`⇔3x=2+40`
`⇔3x=42`
`⇔x=42:3`
`⇔x=14`
Vậy `x=14`
`d)(x+4)(x²-4x+16)-x(x-5)(x+5)=264`
`⇔x³+64-x(x²-25)=264`
`⇔x³+64-x³+25x=264`
`⇔(x³-x³)+25x+64=264`
`⇔25x+64=264`
`⇔25x=264-64`
`⇔25x=200`
`⇔x=200:25`
`⇔x=8`
Vậy `x=8`
`e)(x-2)³-(x-2)(x²+2x+4)+6(x-2)(x+2)=6`
`⇔x³-6x²+12x-8-(x³-8)+6(x²-4)=6`
`⇔x³-6x²+12x-8-x³+8+6x²-24=6`
`⇔(x³-x³)+(-6x²+6x²)+12x+(-8+8-24)=6`
`⇔12x-24=6`
`⇔12x=6+24`
`⇔12x=30`
`⇔x=30/12`
`⇔x=5/2`
Vậy `x=5/2`
`f)(5x-1)²-(5x-4)(5x+4)=7`
`⇔25x²-10x+1-(25x²-16)=7`
`⇔25x²-10x+1-25x²+16=7`
`⇔(25x²-25x²)-10x+(1+16)=7`
`⇔-10x+17=7`
`⇔-10x=7-17`
`⇔-10x=-10`
`⇔x=(-10):(-10)`
`⇔x=1`
Vậy `x=1`
