Question: Factorise 9x²-81
This question can be solved by using a^2-b^2 formula
\[ 9x^2-81=(3x)^2-(9)^2 \]
\[ =(3x-9)(3x+9) \]
\[ =9(x-3)(x+3) \]
So, this is the factorisation of the term.
a^2-b^2 formula is to be used for this question.. Lastly common factor is to be taken out. Also we can such type Factorise 9x²-81 or x^2-64 etc ,
So, such questions seem difficult but are easy to tackle