Page:The Algebra of Mohammed Ben Musa (1831).djvu/40

 If the instance be: “ten and thing to be multiplied by ten,” then you take ten times ten, which is a hundred, and thing by ten is ten things positive; so that the product is a hundred plus ten things.

If the instance be: “ten and thing to be multiplied by itself,” then ten times ten is a hundred, and ten times thing is ten things; and again, ten times thing is ten things; and thing multiplied by thing is a square positive, so that the whole product is a hundred dirhems and twenty things and one positive square.

If the instance be: “ten minus thing to be multiplied by ten minus thing,” then ten times ten is a hundred; and minus thing by ten is minus ten things; and again, minus thing by ten is minus ten things. But minus thing multiplied by minus thing Is a positive square. The product is therefore a hundred and a square, minus twenty things.

In like manner if the following question be proposed to you: “one dirhem minus one-sixth to be multiplied by one dirhem minus one-sixth;” that is to say, five-sixths by themselves, the product is five and twenty parts of a dirhem, which is divided into six and thirty parts, or two-thirds and one-sixth of a sixth. Computation: You multiply one dirhem by one dirhem, the