Factorise the following using completing square method?
9x^2 -9(a+b)x +(2a^2+5ab+2b^2)
2 Answers
Explanation:
.
This seems to be in the form of:
Let's factor out
Now, it looks like it has the following burried in the expression:
Since
Let's divide both sides by
Now, if we write the expression as:
the expression is unchanged and we can write it as:
Explanation:
Given:
9x^2-9(a+b)x+(2a^2+5ab+2b^2)
In the following we premultiply by
A^2-B^2 = (A-B)(A+B)
with
We find:
4(9x^2-9(a+b)x+(2a^2+5ab+2b^2))
=36x^2-36(a+b)x+(8a^2+20ab+8b^2)
=(6x)^2-2(6x)(3a+3b)+(9a^2+18ab+9b^2)-(a^2-2ab+b^2)
=(6x-(3a+3b))^2-(a-b)^2
=(6x-(3a+3b)-(a-b))(6x-(3a+3b)+(a-b))
=(6x-4a-2b)(6x-2a-4b)
=4(3x-2a-b)(3x-a-2b)
So:
9x^2-9(a+b)x+(2a^2+5ab+2b^2) = (3x-2a-b)(3x-a-2b)