Question

Solve for x: x2+8=-1(x square plus eight equals minus one)

Answer 1

[tex] x^{2} +8 = -1 or, x^{2} = -9 [/tex]
we know that the square of any number will be +ve.
but given that -ve. it means number will be imaginary  
so,  $x= \sqrt{-9} = \sqrt{ 3^{2} *(-1)} =3i$

Answer 2

x^2+8=-1
adding -8 on both sides
x^2+8-8=-1-8
x^2=-9
x=√-9
x=3i