Đáp án:
Giải thích các bước giải:
a) x(5-2x) + 2x(x-1) = 15
⇒5x - 2x² + 2x² - 2x = 15
⇒3x = 15
⇒x=5
b) 2x(x-5) - x(3+2x) = 26
⇒2x² - 10x - 3x - 2x² = 26
⇒-13x = 26
⇒x = -2
c) 5x(1-2x) - 3x(x+18) = 0
⇒5x - 10x² - 3x² - 54x = 0
⇒-13x² - 49x = 0
⇒-x(13x + 49) = 0
⇒\(\left[ \begin{array}{l}x=0\\13x=-49\end{array} \right.\)
⇒\(\left[ \begin{array}{l}x=0\\x=-\frac{49}{3}\end{array} \right.\)
d) 3x(12x - 4) - 9x(4x - 3) = 30
⇒36x² - 12x - 36x² + 27x = 30
⇒15x = 30
⇒x = 2
e) 3(5x - 1) - x(x - 2) + x² - 13x = 7
⇒15x - 3 - x² + 2x + x² - 13x = 7
⇒4x - 3 = 7
⇒4x = 10
⇒x = $\frac{5}{2}$
f) 4(x + 2) - 7(2x - 1) + 9(3x - 4) = 30
⇒4x + 8 - 14x + 7 + 27x - 36 = 30
⇒17x - 21 = 30
⇒17x = 51
⇒x = 3
