Substitusikan x = $-$2 ke dalam bentuk aljabar.

P = x⁴ + 12x² $-$ 8x

= ($-$2)⁴ + 12($-$2)² $-$ 8($-$2)

= 16 + 12$\times$4 + 16

= 16 + 48 + 16 = 80

Q = 3x $-$ 16 = (3 $\times$ ($-$2)) – 16 = $-$6 $-$ 16 = $-$22

P $-$ Q = 80 – ($-$22) = 80 + 22 = 102