Microsoft Excel is WRONG!!! Beware...
never and ever a minus signed number could give a minus signed number when squared.
-5 *-5= -5^2= 25
because -25^0.5 or the square root of -25 could not be solve with real numbers
That is the conceptual error, you dont need a Doctor help , you need to go again to your's junior hig scholl , give back your all titles and diploma to the janitrol , sit down at the first chair and try to learn elementary algebra or arithmetic, wichever you want to call it