3x( 3x+ 3) = (2x + 5)( 5x - 7)
9x² + 9x = 10x² - 14x + 25x - 35
9x² + 9x = 10x² + 11x - 35
9x² + 9x - 10x² - 11x + 35 = 0
- x² - 2x + 35 = 0
x² + 2x - 35 = 0
D = b² - 4ac = 4 - 4 × (-35) = 4 + 140 = 144 = 12²
x1 = ( - 2 + 12) / 2 = 5
x2 = ( - 2 - 12) / 2 = - 7