10. B
(2x - 3y)² = (2x)^2 - 2.2x.3y + (3y)² = 4x² - 12xy + 9y²
11 B
9x² + 30x + 25 = 9x² + 30x + 5² = (3x)^2 + 2.3x.5 + 5² = (3x+5)²
12. C
-8x³ + 12x²y - 6xy² + y³ = (-2x + y)³
13. B
(1/2x² + 1/3)³ = $1/8x^6 + 1/4x^4y + 1/6x²y² + 1/27y³$
14. A
3x - 3x² + x³ - 1 = (x - 1)³
15. B
(a + b)³ + (a - b)³ - 6ab² = 2a³