1.1) (c-6)² = c² + 36 - 12c

2) (2a-3b)² = (2a)² + (3b)² - 2×3×ab = 4a² + 9b² - 12ab

3) (5-a)(5+a) = 25 - a²

4) (7x+10y)(10y-7x) = (10y)² - (7x)² = 100y² - 49x²

2. 1) b²- 49 = b² - 7² = (b-7)(b+7)

2) c² - 8c + 16 = c² - 2×4×c + 4² = (c-4)²

3) 100-9x² = 10² - (3x)² = (10-3x)(10+3x)

4) 4a² + 20ab + 25b² = (2a)² + 2×2×5×ab + (5b)² = (2a+5b)²

3. (x-2)(x+2) - (x-5)² = (x²-2²) - (x²+25-10x) = x²-4-x²-25-10x = -29-10x