Respuesta :

For this case we must find an equation equivalent to:

[tex]\sqrt {x ^ 2 + 81} = x + 10[/tex]

We square both sides of the equation to eliminate the root:

[tex]x ^ 2 + 81 = (x + 10) ^ 2[/tex]

We have by definition that:

[tex](a + b) ^ 2 = a ^ 2 + 2ab + b ^ 2[/tex]

So, rewriting the right side of the equation we have:

[tex]x ^ 2 + 81 = x ^ 2 + 2 * 10 * x + 10 ^ 2\\x ^ 2 + 81 = x ^ 2 + 20x + 100[/tex]

ANswer:

Option D