y = x^4 + 2x^2 - 1
The first think I always do in such a question is get the graph.
Go to wolfranalpha.com and see the graph to tell me what I'm looking for.
Put y = x^4 + 2x^2 - 1 into the input bar. You find out that there are only 2 answers.
Use the Quadratic Formula
a = 1
b = 2
c = - 1
Then let z = x^2
So the new equation is
y = z^2 + 2x - 1
You solve for z and you get
z1 = 0.4142 and z2 = - 2.4142 You can go no further with z2 because the square root of a minus number can't be graphed on the coordinate system.
z = x^2
0.4142 = x^2
x = +/- 0.6435
Note to moderator
When I send a student to wolframalpha, the work is mine and I'm not copying and pasting anything that isn't allowed by wolfram