Question

Solve the equation: 7x^2 = -91

Answer 1

7x^2 = -91
x^2 = -91/7
x^2 = -13
x^2 = +/- root(-13)

Answer 2

\[ \left\{\left\{x\to -i \sqrt{13}\right\},\left\{x\to i \sqrt{13}\right\}\right\} \]

Answer 3

what's the i before the 13?

Answer 4

\[ \sqrt{-1} = i \] Read more here: http://en.wikipedia.org/wiki/Complex_number