Brahmagupta

The sum of two positive quantities is positive; of two negative is negative; of a positive and a negative is their difference; or, if they are equal, zero.

In subtraction, the less is to be taken from the greater, positive from positive; negative from negative.

The product of a negative quantity and a positive is negative; of two negatives, is positive; of two positives, is positive.

Positive, divided by positive, or negative by negative, is positive. Zero, divided by zero, is zero. Positive, divided by negative, is negative.

The square of negative or positive is positive; of zero, is zero. The root of a square is such as was that from which it was raised [i.e. either positive or negative]. (37).