`a)`
`3(x+1)^2+(x-5)^2=4(x+3)(x-1)`
`\to 3(x^2+2x+1)+(x^2-10x+25)=4(x^2+2x-3)`
`\to 3x^2+6x+3+x^2-10x+25=4x^2+8x-12`
`\to (3x^2+x^2)+(6x-10x)+(3+25)=4x^2+8x-12`
`\to 4x^2-4x+28=4x^2+8x-12`
`\to 4x^2-4x^2-4x-8x=-12-28`
`\to -12x=-40`
`\to x=10/3`
Vậy `x=10/3`
`b)`
`(2x-1)^2+(x+3)^2-5(x+7)(x-7)=0`
`\to (4x^2-4x+1)+(x^2+6x+9)-5(x^2-49)=0`
`\to 4x^2-4x+1+x^2+6x+9-5x^2+245=0`
`\to (4x^2+x^2-5x^2)+(6x-4x)+(1+9+245)=0`
`\to 2x+255=0`
`\to 2x=-255`
`\to x=-255/2`
Vậy `x=-255/2`
`c)`
`(4x-1)^2-3x(x+3)=-12`
`\to (16x^2-8x+1)-(3x^2+9x)=-12`
`\to 16x^2-8x+1-3x^2-9x+12=0`
`\to (16x^2-3x^2)+(-8x-9x)+(1+12)=0`
`\to 13x^2-17x+13=0`
mà `13x^2-17x+13\ne0`
Vậy phương trình vô nghiệm
`d)`
`(3x-2)(9x^2+6x+4)-27x(x^2-3)=6`
`\to (3x)^3-2^3-27x^3+81x=6`
`\to 27x^3-8-27x^3+81x=6`
`\to 81x-8=6`
`\to 81x=14`
`\to x=14/81`
Vậy `x=14/81`
