Page:Cowie's Printer's pocket-book and manual.djvu/73

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+ plus, or more, is the sign of real existence of the quantity it stands before, and is called an affirmative or positive sign. It is also the mark of addition: thus a + b, or 6 + 9, implies that a is to be added to b, or 6 added to 9.

− minus, or less, before a single quantity, is the sign of negation or negative existence, shewing the quantity to which it is prefixed to be less than nothing. But between quantities it is the sign of substraction; thus, a − b, or 8 − 4, implies b substracted from a, or 8 after 4 has been substracted.

= equal. The sign of equality, though Des Cartes and some others use this mark ; thus, signifies that a is equal to b. Wolfius and some others use the mark = for the identity of ratios.

× into, or with. The sign of multiplication, shewing that the quantities on each side the same are to be multiplied by one another, as a × b is to be read, a multiplied into b; 4 × 8, the product of 4 multiplied into 8. Wolfius and others make the sign of multiplication a dot between the two factors; thus, 7. 4 signifies the product of 7 and 4. In algebra the sign is commonly omitted, and the two quantities put together; thus, b d expresses the product of b and d. When one or both of the factors are compounded of several letters, they are distinguished by a line drawn over them; thus the factum of a + b − c into d, is wrote d × $\overline{a + b − c}$. Leibnitz, Wolfius, and others, distinguish the compound factors, by including them in a parenthesis thus (a + b − c) d.

÷ by. The sign of division; thus, a ÷ b denotes the quantity a to be divided by b. Wolfius makes the sign of division two dots; thus, 12 : 4 denotes the quotient of 12 divided by 4 = 3. If either the divisor or dividend, or both