Question

x^2-9=5x+15

Answer 1

=> x² - 9 - 5x - 15 = 0

=> x² - 5x - 24 = 0

=> x² - 8x + 3x - 24 = 0 

=> x(x - 8) + 3(x - 8) = 0

=> (x + 3)(x - 8) = 0

=> x + 3 = 0 => x = -3

hoặc x - 8 = 0 => x = 8

Vậy x = -3 ; x = 8

Answer 2

x²-9=5x-15

\(\Leftrightarrow\) (x+3)(x-3)-5(x+3)=0

\(\Leftrightarrow\) (x+3)(x-3-5)=0

\(\Leftrightarrow\) (x+3)(x-8)=0

\(\Leftrightarrow\) x=-3 hoặc x=8

Vậy...