Question

How do you find all the zeros of `f(x)=x^4-5x^2-36`?

Answer 1

`x={-3,-2,2,3}`

Explanation:

let `u=x^2` then `f(x)=x^4-5x^2-36 ->f(u)=u^2-5u-36`
`u^2-5u-36=0`
`(u-9)(u+4)=0`
`u-9=0,u+4=0`
`u=9 or u=-4`
`x^2=9,x^2=4`
`x=+-3,x=+-2`
`x={-3,-2,2,3}`