-Square root 25= ?

Question

I have this problem on my homework and I wrote that the answer was +/-5 because

-(+5)=-5 and -(-5)=+5.  Was marked wrong and told the answer is -5.

Why?

Answer 1

-√25=-5 because √25=5 only, not -5 also because √ denotes the principal or nonnegative square root of 25