Answer:
d
Step-by-step explanation:
Factoring using difference of squares
a² - b² = (a - b)(a + b)
a
x² - 1
= x² - 1²
= (x - 1)(x + 1)
b
x² - y²
= (x - y)(x + y)
c
x² - 4
= x² - 2²
= (x - 2)(x + 2)
d
4 - 16y ← 16y is not a perfect square and so cannot be factored
If it was 4 - 16y² then it could be factored using difference of squares
