1) (x - y)(x + y) = x² - y²

2) a² - c² = (a - c)(a + c)

3) (10 + a)(a - 10) = (a + 10)(a - 10)

4) p² + q² = (p - q)(p + q)

5) 25m² - 16n² = (5m)² - (4n)² = (5m - 4n)(5m + 4n)

6) (a - b)(a + b) = a² - b²

7) 4a² - 1 = (2a)² - 1² = (2a - 1)(2a + 1)

8) (3t + 2)(2 - 3t) = (2 + 3t)(2 - 3t) = 2² - (3t)² = 4 - 9t²

9) x² + 4 = невозможно

10) 9k² - 49 = (3k)² - 7² = (3k - 7)(3k + 7)

11) (c - d)(c + d) = c² - d²

12) 100 - x² = 10² - x² = (100 - x)(100 + x)

13) (3 + q)(q - 3) = (q + 3)(q - 3) = q² - 3² = q² - 9

14) 1 + x² = невозможно

15) m² - 4 = m² - 2² = (m - 2)(m + 2)