Question

What substitution should be used to rewrite 4x^4-21x^2+20=0 as a quadratic function?

Answer 1

refer the explanation

Explanation:

this question can be written as

X^2=y

so,x^4=y^2

so it will be 4y^2-21y+20=0

Answer 2

see explanation

Explanation:

Let u = x² ( choice of variable is flexible ), then

4u² - 21u + 20 = 0 ← expressed as a quadratic

This can now be solved for u and converted back into terms of x