can't factor
use quadratic
for
ax^2+bx+c=0
x=[tex] \frac{-b+/- \sqrt{b^2-4ac} }{2a} [/tex]
given
1x^2-4x+85=0
a=1
b=-4
c=85
x=[tex] \frac{-(-4)+/- \sqrt{(-4)^2-4(1)(85)} }{2(1)} [/tex]
x=[tex] \frac{4+/- \sqrt{16-340} }{2} [/tex]
x=[tex] \frac{4+/- \sqrt{-324} }{2} [/tex]
x=[tex] \frac{4+/- (\sqrt{-1})(\sqrt{324}) }{2} [/tex]
remember that √-1=i
x=[tex] \frac{4+/- i(\sqrt{324}) }{2} [/tex]
x=[tex] \frac{4+/- i(18) }{2} [/tex]
x=2+/-9i
x=2+9i or x=2-9i
