Question 186742
Bob was thinking of a number between 5 and 15 that when squared and added
 to 23 equals the next number's square. What is the number? 
:
You can write it:
x^2 + 23 = (x+1)^2
FOIL
x^2 + 23 = x^2 + 2x + 1
:
23 - 1 = x^2 - x^2 + 2x
:
22 = 2x
:
x = 11
;
:
Check
 11^2 + 23 = 144
12^2 = 144