ok when I was working it out for 27=c^2 my answer was c=3 square root of 3, -3 square of 3
and that was the same answer for 18+9=c^2 was the same answer as 27=c^2
(9)^2+(3)^2=c^2 the answer I got for that was c= 3 square root of 10, -3 square root of 10 I hope its right and can help you