added way to send error for when dividing by zero

[ChrisTienYenWalker]

For this pull request I made changes to ensure that the program will not crash when dividing by zero.
if (b == 0) {
throw new IllegalArgumentException("Divisor cannot be zero.");
}
I tossed that if statement in every function for diving by zero
This is because you can't divide by 0, and since b is always the denominator, I can run a if statement on b

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