Factorize:
(i) `4\ (x+y)^2-28 y(x+y)+49 y^2`
(ii) `(2a+3b)^2+2(2a+3b)(2a-3b)+(2a-3b)^2`

Explanation

Let's solve the given problems step by step.

### (i) Factorize:
`4(x+y)^2 - 28y(x+y) + 49y^2`

**Step 1: Identify the structure of the expression.**
The expression resembles a quadratic in terms of `(x+y)`. We can rewrite it as:
`4[(x+y)^2 - 7y(x+y) + \frac{49}{4}y^2]`
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