4b^2-4b+1

2^2 b^2 -2 × 2b × 1 + 1^2

(2b)^2 - 2×2b×1+1^2

(2b-1)^2

1-16b^2

1^2 - 4^2 b^2

1^2 - (4b)^2

(1-4b)×(1+4b)

49a^2 - 100

7^2a^2-10^2

(7a)^2-10^2

(7a-10) × (7a+10)