Factorize each of the following expressions:
(1)`x^4-625`
(2) `x^4-1`
(3)`49(a-b)^2-25(a+b)^2`
(4) `x-y-x^2+y^2`

Explanation

Let's factorize each of the given expressions step by step.

### (1) Factorize `x^4 - 625`

**Step 1:** Recognize that this is a difference of squares. We can express it as:
\[ x^4 - 625 = (x^2)^2 - (25)^2 \]

**Step 2:** Apply the difference of squares formula, which states that \( a^2 - b^2 = (a - b)(a + b) \):
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