Đáp án+Giải thích các bước giải:
`b)`
`3(x+2)^(2)-3x(x+1)=15`
`⇔3(x^(2)+4x+4)-3x^(2)-3x=15`
`⇔3x^(2)+12x+12-3x^(2)-3x-15=0`
`⇔9x-3=0`
`⇔x=1/3`
Vậy `x=1/3`
`c)`
`3(x+2)^(2)+(2x-1)^(2)-7(x^(2)-9)=36`
`⇔3(x^(2)+4x+4)+4x^(2)-4x+2-7x^(2)+63=36`
`⇔3x^(2)+12x+12+4x^(2)-4x+1-7x^(2)+63-36=0`
`⇔8x+40=0`
`⇔x=-5`
Vậy `x=-5`
`d)`
`(5x-1)^(2)-(5x-4)(5x+4)=7`
`⇔25x^(2)-10x+1-25x^(2)+16-7=0`
`⇔-10x+10=0`
`⇔x=1`
Vậy `x=1`
