Đáp án + Giải thích các bước giải:
a, `2x(5-6x)+3x(4x-5)-2(x-7) = 30`
`=> 10x - 12x^2 + 12x^2 - 15x - 2x + 14 = 30`
`=> (12x^2-12x^2) - (15x-10x+2x) + 14 = 30`
`=> -7x + 14 = 30`
`=> -7x = 16`
`=> x = -16/7`
Vậy `x \in {-16/7}`
b, `3x(x+1)-2x(x+2)=(x-5)^2`
`⇒ 3x^2 + 3x - 2x^2 - 4x = x^2 - 10x + 25`
`=> 3x^2 + 3x - 2x^2 - 4x - x^2 + 10x- 25 = 0`
`=> (3x^2-2x^2-x^2) + (10x-4x+3x) - 25 = 0`
`=> 9x - 25 = 0`
`=> 9x = 25`
`=> x = 25/9`
Vậy `x \in {25/9}`
c, `5x-3(5x-2)=6-5^2`
`=> 5x - 15x + 6 = -19`
`=> -10x + 6 = -19`
`=> -10x = -25`
`=> x = 5/2`
Vậy `x \in {5/2}`
d, `(x-1)(x^2+x+1)-2(5x-3)=(x+5)(x^2-5x+25)`
`=> x^3 - 1 - 10x + 6 = x^3 + 125`
`=> x^3 - 1 - 10x + 6 - x^3 - 125 = 0`
`=> (x^3-x^3) - 10x - (125-6+1) = 0`
`=> -10x - 120 = 0`
`=> -10x = 120`
`=> x = -12`
Vậy `x \in {-12}`
