Answer:
last option
x² + 81 = x² + 20x + 100
Step-by-step explanation:
[tex] \sqrt{ {x}^{2} + 81 } = x + 10 \\ [/tex]
squaring both sides
[tex] (\sqrt{ {x}^{2} + 81 } )^{2} = {(x + 10) }^{2} \\ {x}^{2} + 81 = {(x + 10)}^{2} [/tex]
using the identity
(a + b)² = a² + b² + 2ab
for (x + 10) ²
[tex] {x}^{2} + 81 = {x}^{2} + 20x + 100[/tex]
hence, option D
