a) 2x² + 3(x-1)(x+1) - 5x(x+1)
= 2x² + 3(x² - 1) - 5x² - 5x
= 2x² + 3x² - 3 - 5x² - 5x
= (2x² + 3x² - 5x²) - 5x - 3
= -5x - 3
b) (8-5x)(x+2) + 4(x-2)(x+1) + 2(x-2)(x+2) + 10
= 8x + 16 - 5x² - 10x + 4(x² + x - 2x - 2) + 2(x² - 4) + 10
= 8x + 16 - 5x² - 10x + 4x² + 4x - 8x - 8 + 2x² - 8 + 10
= (-5x² + 4x² + 2x²) + (8x - 10x + 4x - 8x) + (16 - 8 - 8 + 10)
= x² - 6x + 10
c) 4(x-1)(x+5) - (x+2)(x+5) - 3(x-1)(x+2)
= 4(x² + 5x - x - 5) - (x² + 5x + 2x + 10) - 3(x² + 2x - x - 2)
= 4x² + 20x - 4x - 20 - x² - 5x - 2x - 10 - 3x² - 6x + 3x + 6
= (4x² - x² - 3x²) + (20x - 4x - 5x - 2x - 6x + 3x) + (-20 - 10 + 6)
= 6x - 24
