#### Answer

$c\approx6.4\text{ or }c\approx-6.4$

#### Work Step by Step

We start with the given equation: $5^2+4^2=c^2$
To simplify each of the constants being squared, we multiply them by themselves: $25+16=c^2$
We simplify on the left side of the equation by adding: $41=c^2$
To solve the equation $41=c^2$, we must perform the opposite operation of squaring, which is taking the square root, in order to clear the exponent: $$41=c^2$$$$\sqrt {41}=\sqrt {c^2}$$$$c\approx\pm6.4$$$$c\approx6.4\text{ or }c\approx-6.4$$