The elements of that mathematical art commonly called algebra, expounded in two books / By John Kersey ... To which is added lectures read in the School of Geometry in Oxford, concerning the geometrical construction of algebraical equations; and the numerical resolution of the same by the compendium of logarithms. By Dr. Edmund Halley.

Kersey, John, 1616-1690?

Date:: 1717

Credit: The elements of that mathematical art commonly called algebra, expounded in two books / By John Kersey ... To which is added lectures read in the School of Geometry in Oxford, concerning the geometrical construction of algebraical equations; and the numerical resolution of the same by the compendium of logarithms. By Dr. Edmund Halley. Source: Wellcome Collection.

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$More Examples of the Rule of Addition in the foregoing Se£h Ilf; To be added, 5* 3* — 5 aa — 2 aa . “F 7 ab 4* 13 ab The Sum, da — 7 aa i ft- 20ab ac • —• 3 bed + 3<*J To be added, < 2 ac — bed + 2^5 L 7,ac — 6 bed 4- The Sum, 6ac — iobed 1 + 12 a* IV. When two fimple Quantities propos’d to be added together be like, and have equal Numbers prefix'd, but unlike or contrary Signs, the Sum will be o, or nothing 5 for the affirmative Quantity will deftroy or extinguifli the Negative • As for Example, if it be required to add c, or -f-c, to —c, the Sum will be o$ to wit, nothing. For fuppofing Add, —c, or — ic to be a Debt of one Crown that I owe $ and -fc, or 4~ic to be one Crown in my Purfe, it is evident that Sum, one Crown in ready Money will difcharge or ftrike off a Debt of one Crown ^ and fo that Debt and Credit being added or compared together, thfc Sum amounts to o. In like manner, if it be defired to add —6 l. to -\-6 l. the Sum will be o 5 for if my whole Eltatebe worth but £ Pounds, and. I owe a Debt of 6 Pounds, it is manifeft that my clear Eftate is worth or Add, amounts to juft nothing. Sum, More Examples of the Rule of Addition in the preceding Se&.-IV. To be added, j + — 5 abc 4- 5abc -j- 7 ddd — 7 ddd The Sum, 0 . . ■ 0 —-> 1 0 V. When two fimple Quantities propos’d to be added together be like, but their Signs unlike, and the prefixed Numbers unequal between themlelves^ firft fubtra£l the leffer Number prefixed from the greater, then to the Remainder annex the Letter or Letters by which either of the Quantities propofed is expreft ; laftly, before the faid Remainder fet the Sign which ftands before the greater Number prefix’d, fo fiiall this new Quantity be the Sum defired. As for Example, if it be defired to add -—2a to C -p 30 4-^30, the Sum will be a. For firft Subtracting 2 Add, < —2'a from 3 the Remainder is 1, to which annexing a and £--—*- prefixing ft- (becaufe -f belongs to that Quantity Sum, 4- ia, or, \ a which has the greater Number prefix’d^ there arifes -fitf, or -\-a for the Sum' fought. Again, to add -\-b to —3 £, I fubtraSl 1 the leffer Number prefix’d, from 3 the greater,* and to the C — 3h Remainder 2 annexing b and prefixing—, ( becaule Add, < b — belongs to 3^ whofe prefix’d Number 3 is greater £- than that of -\-b or -\-ib )\ find —2b for the Sum, — 2b Sum defiredv Thus you fee that this laftRule of Addition is performed bySubtra&ion,and may eafilv ‘ be underftood under the Notion of difcharging or paying oft a Debt, or at leaft part of a Debt by fo much ready Money or Credit,and then obferving what Debt remains unpaid, B of$

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