Tìm các số thực x, biết:

a) (2x – 3)²– 49 = 0

b) 2x(x – 5) – 7(5 – x) = 0

c) x²– 3x – 10 = 0

Hướng dẫn giải

a) (2x – 3)²– 49 = 0

⇔ (2x – 3)²– 7²= 0

⇔ (2x – 3 – 7)(2x – 3 + 7) = 0

⇔ (2x – 10)(2x + 4) = 0

$\Leftrightarrow \left[ \begin{array}{l}2x - 10 = 0\\2x + 4 = 0\end{array} \right.$

$\Leftrightarrow \left[ \begin{array}{l}x = 5\\x = - 2\end{array} \right.$

Vậy x = 5, x = - 2.

b) 2x(x – 5) – 7(5 – x) = 0

⇔ 2x(x – 5) + 7(x – 5) = 0

⇔ (x – 5)(2x + 7) = 0

$\Leftrightarrow \left[ \begin{array}{l}x - 5 = 0\\2x + 7 = 0\end{array} \right.$

$\Leftrightarrow \left[ \begin{array}{l}x = 5\\x = - \frac{7}{2}\end{array} \right.$

Vậy $x = - \frac{7}{2}$, x = 5.

c) x²– 3x – 10 = 0

⇔ x²– 5x + 2x – 10 = 0

⇔ x(x – 5) + 2(x – 5) = 0

⇔ (x – 5)(x + 2) = 0

$\Leftrightarrow \left[ \begin{array}{l}x - 5 = 0\\x + 2 = 0\end{array} \right.$

$\Leftrightarrow \left[ \begin{array}{l}x = 5\\x = - 2\end{array} \right.$

Vậy x = 5, x = – 2.