Question

When must a system of linear equations be solved algebraically, not graphically?

Answer 1

The correct answer is the Option "A": Integer. Then, the text is: "Whenever the solution to a system does not have integer coordinates, it can be difficult or impossible to find the precise answer through graphing."
 
 By definition, the numbers called "Integers" are all the positive numbers (which are known as "Natural numbers"), all the negative numbers and the zero (0) and they are identified with the letter "Z": 
 
 Z= {-∞...-3,-2,-1,0,1,2,3...+∞}