Question

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

Answer 1

can't factor
use quadratic
for
ax^2+bx+c=0
x=
`(-b+/- √(b^2-4ac) )/(2a)`

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

x=
`(-(-4)+/- √((-4)^2-4(1)(85)) )/(2(1))`
x=
`(4+/- √(16-340) )/(2)`
x=
`(4+/- √(-324) )/(2)`
x=
`(4+/- (√(-1))(√(324)) )/(2)`
remember that √-1=i
x=
`(4+/- i(√(324)) )/(2)`
x=
`(4+/- i(18) )/(2)`
x=2+/-9i

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