For what values (cases) of the variables the expression does not exist: a/a-b

The cases are when a-b = 0 and when a = b

Step-by-step explanation:

An expression is termed as undefined (not to exist) if the denominator of the expression is zero. Given the expression a/a-b, the denominator of the expression is a-b. For the expression to be undefined, the expression at the denominator must be equal to zero i.e a-b = 0

If a - b = 0, then a = 0+b; a = b

Another case for the function not to exist is if a = b

51

step-by-step explanation:

73-22=51 the   mass number minus the amount of protons gives you the amount of neutrons