1. ## Polynomials

How to factorise (a^4) - (7a^2 x b^2)- 18b^4??
Can show me step by step??

2. Originally Posted by maybeline9216
How to factorise (a^4) - (7a^2 x b^2)- 18b^4??
Can show me step by step??

Let $\displaystyle A = a^2$ and $\displaystyle B = b^2$.

So we have $\displaystyle A^2 - 7AB - 18B^2$.

You should be able to factorise this by inspection...

$\displaystyle (A-9B)(A+2B)$

$\displaystyle (a^2 - 9b^2)(a^2 + 2b^2)$

Now you have a Difference of Two Squares as the first factor. Factorising that gives

$\displaystyle (a + 3b)(a - 3b)(a^2 + 2b^2)$.