Question

Решить рівняння(х+3)(3х-7)=0

Answer 1

$(x+3)(3x-7)=0\\3x^2-7x+9x-21=0\\3x^2+2x-21=0\\D = 2^2-4*3*(-21)=4+252=256\\x_1=\frac{-2-\sqrt{256} }{2*3} = \frac{-2-16 }{6} = \frac{-18}{6} = -3\\x_2 = \frac{-2+\sqrt{256} }{2*3} = \frac{-2+16 }{6} = \frac{14}{6} = = \frac{7}{3} = 2\frac{1}{3}$