OK, the equation is: y = x^4 - 18x^2 + 56.
And you want to find where the graph cuts the x-axis, which is where y = 0. This gives us,
x^4 - 18x^2 + 56=0
let u = x^2, then
u^2 - 18u + 56 = 0
(u - 4)(u - 14) = 0
So, u = 4, u = 14
Or, x^2 = 4, x^2 = 14
i,e, x + 2, x = -2, x = sqrt(14), x = -sqrt(14)