Question

tìm x biết x(x-15)=-50

Answer 1

x(x - 15) = -50

x² - 15x + 50 = 0

x² - 10x - 5x + 50 = 0

(x² - 10x) - (5x - 50) = 0

x(x - 10) - 5(x - 10) = 0

(x - 10)(x - 5) = 0

x - 10 = 0 hoặc x - 5 = 0

*) x - 10 = 0

x = 0 + 10

x = 10

*) x - 5 = 0

x = 0 + 5

x = 5

Vậy x = 10; x = 5

Answer 2

\(x^2-15x=-50\)

\(x^2-2.x.\dfrac{15}{2}+\dfrac{225}{4}=\dfrac{25}{4}\)

\(\left(x-\dfrac{15}{2}\right)^2=\left(\dfrac{5}{2}\right)^2\)

\(\Leftrightarrow\left[{}\begin{matrix}x=10\\x=5\end{matrix}\right.\)