What substitution should be used to rewrite 4x4 – 21x2 + 20 = 0 as a quadratic equation?

u = x2
u = 2x2
u = x4
u = 4x4

Consider the equation

We have to rewrite this equation as quadratic equation.

A quadratic equation is of the form , where 'a', 'b' and 'c' are the real numbers.

The given equation can be expressed as ,

Let u = in the given equation, we get

is the required quadratic equation.

Therefore, u = has changed the given equation into quadratic equation.

So, Option 1 is the correct answer.

the answer is (2x+8)²= 16