We have to solve for c:
[tex](c+9)^2=64[/tex]
When we have quadratic expressions, we have to take into account that each number has two possible square roots: one positive and one negative.
We can see it in this example: the square root of 4 can be 2 or -2. This is beacuse both (-2)² and 2² are equal to 4.
Then, taking that into account, we can solve this expression as:
[tex]\begin{gathered} (c+9)^2=64 \\ c+9=\pm\sqrt[]{64} \\ c+9=\pm8 \end{gathered}[/tex]
We then calculate the first solution for the negative value -8:
[tex]\begin{gathered} c+9=-8 \\ c=-8-9 \\ c=-17 \end{gathered}[/tex]
And the second solution for the positive value 8:
[tex]\begin{gathered} c+9=8 \\ c=8-9 \\ c=-1 \end{gathered}[/tex]
Then, the two solutions are c = -17 and c = -1.
We can check them replacing c with the corresponding values we have found:
[tex]\begin{gathered} (-17+9)^2=64 \\ (-8)^2=64 \\ 64=64 \end{gathered}[/tex][tex]\begin{gathered} (-1+9)^2=64 \\ (8)^2=64 \\ 64=64 \end{gathered}[/tex]
Both solutions check the equality, so they are valid solutions.
Answer: -17 and -1.
