Giải thích các bước giải :
`↓↓↓`
Bài `1` :
a, `7x - 8 = 4x + 7`
`⇔ 7x = 4x + 15`
`⇔ 3x = 15`
`⇔ x = 5`
Vậy `...`
b, `2x + 5 = 20 - 3x`
`⇔ 2x + 5 = -3x + 20`
`⇔ 2x = -3x + 15`
`⇔ 5x = -3x + 15 + 3x`
`⇔ 5x = 15`
`⇔ x = 3`
Vậy `...`
c, `x^2 + x - 12 = 0`
`⇔ x^2 + x - ( 3 . 4 ) = 0`
`⇔ ( x - 3 )( x + 4 ) = 0`
⇔ \(\left[ \begin{array}{l}x-3=0\\x+4=0\end{array} \right.\)
⇔ \(\left[ \begin{array}{l}x=3\\x=-4\end{array} \right.\)
Vậy `...`
d, `6x^2 - 11x - 10 = 0`
`⇔ 6x^2 - 15x - 4x - 10 = 0`
`⇔ 6x^2 + 4x - 15x - 10 = 0`
`⇔ 2x(3x+2)-5(3x+2)=0`
`⇔ (2x-5)(3x+2)=0`
⇔ \(\left[ \begin{array}{l}2x-5=0\\3x+2=0\end{array} \right.\)
⇔ \(\left[ \begin{array}xx = \dfrac{5}{2}\\x=-\dfrac{2}{3}\end{array} \right.\)
