How to factor this ?

Question

Hi, I know how to factor when the exponent is squared but the 4 exponent is confusing me. 

 

x⁴ —13x²+36

Answer 1

Just do it the same way, but the x would now be x²:

 

Such that the answer here there is:

 

(x²-9)(x²-4) *The proof is to try using FOIL on that and it should return to the original expression.*

 

...and you can further factor them through sum&difference:

 

(x+3)(x-3)(x+2)(x-2)