Question

Solve the equation x^2-4x+85=0

Answer 1

Can't factor
use quadratic
for
ax^2+bx+c=0
x=$\frac{-b+/- \sqrt{b^2-4ac} }{2a}$

given
1x^2-4x+85=0
a=1
b=-4
c=85

x=$\frac{-(-4)+/- \sqrt{(-4)^2-4(1)(85)} }{2(1)}$
x=$\frac{4+/- \sqrt{16-340} }{2}$
x=$\frac{4+/- \sqrt{-324} }{2}$
x=$\frac{4+/- (\sqrt{-1})(\sqrt{324}) }{2}$
remember that √-1=i
x=$\frac{4+/- i(\sqrt{324}) }{2}$
x=$\frac{4+/- i(18) }{2}$
x=2+/-9i

x=2+9i or x=2-9i