Answer:
f(x + 4) × f(x) = x^4 + 16x³ + 90x² + 208x + 185
Explanation:
f(x) = x² + 4x + 5
f(x + 4) = (x + 4)² + 4(x + 4) + 5
f(x + 4) × f(x) =
= (x² + 4x + 5)[(x + 4)² + 4(x + 4) + 5]
= (x² + 4x + 5)[x² + 8x + 16 + 4x + 16 + 5]
= (x² + 4x + 5)(x² + 12x + 37)
= x^4 + 12x³ + 37x² + 4x³ + 48x² + 148x + 5x² + 60x + 185
= x^4 + 16x³ + 90x² + 208x + 185