can someone help me undo this square root: c^2 = 169?

There are two solutions to that:
13 * 13 = 169
-13 * -13 = 169

To solve this you would take the square root of both sides; but remember the ± sign:
c = ± √169
c = ± 13

Answer:
c = -13 or c = 13

c² = 169

c² - 169 = 0

c² - 13² = 0

(c - 13)(c + 13) = 0

c - 13 = 0 or c + 13 = 0

c = 13 or c = -13

Just square root both sides.

c = +/- sqrt(169)
c = +/- 13

simple as that.

c² = 169
c = ± 13

c = 13.