1) f(2x) = (2x)² - 1 = 4x² - 1
2) f(x+1) - f(x-1) = (x+1)² - 1 - (x-1)² + 1= x² + 2x + 1 - 1 - x² + 2x - 1= 4x
1) f(2x) = (2x)² - 1 = 4x² - 1
2) f(x+1) - f(x-1) = (x+1)² - 1 - (x-1)² + 1
= x² + 2x + 1 - 1 - x² + 2x - 1
= 4x