Question

which substitution should be used to rewrite 4x^4-21x^2+20=0 as a quadratic equation?
u=x^2
u=2x^2
u=x^4
or
u=4x^4

Answer 1

u is not applicable in it because we apply u when the power of x is -1,-2,-3....... but here every value is +2,+4 so we will directly apply formula