f(x+1) = 16(x+1)² - (x+1) = 16(x²+2x+1) - x - 1
= 16x² + 32x + 16 - x - 1 = 16x²+31x+15
so
f(x+1)-f(x) = 16x²+31x+15 - (16x² - x)
= 16x²+31x+15 - 16x² + x
= 32x + 15
