Question

Solve 3x² – 18x + 5 = 47 for x.

A) x= 3±√23

B) x= 3±√51

C) x= 3±√41

D) x= 3±√5

Answer 1

$3x^2-18x + 5 = 47 \\ 3x^2-18x + 5-47=0 \\ 3x^2-18x -42=0 \ \ |:3 \\ x^{2} -6x-14=0 \\ D=b^2-4ac=(-6)^2-4*1*-14=36+56=92\\x= \frac{-bб \sqrt{D} }{2a}= \frac{6б \sqrt{92} }{2}= \frac{6б 2\sqrt{23} }{2}= \frac{2(3б \sqrt{23}) }{2}= 3б \sqrt{23}$

Answer: A.