Solve for x x2+4x-21=0

If I did my math correctly it would be that x=2.04

First you calculate the determinant:

d=b^2-4ac

d=4^2-4*1 * (-21) = 16+84=100

Because d>0 there are two solutions for x:

x_1 = (-b+√d) / 2a = (-4+√100) / 2*1 = 6/2 = 3

x_2 = (-b-√d) / 2a = (-4-√100) / 2*1 = - 14/2 = - 7

The solutions for x is x = 3 and x = - 7