Page:The Algebra of Mohammed Ben Musa (1831).djvu/38

 units, the units by the greater numbers, and the units by the units.

If the units, combined with the greater numbers, are positive, then the last multiplication is positive; if they are both negative, then the fourth multiplication is likewise positive. But,if one of them is positive, and one negative, then the fourth multiplication is negative.

For instance, “ten and one to be multiplied by ten and two.” Ten times ten is a hundred; once ten is ten positive; twice ten is twenty positive, and once two is two positive; this altogether makes a hundred and thirty-two.

But if the instance is “ten less one, to be multiplied by ten less one,” then ten times ten is a hundred; the