. Trigonometria. at proportion the fide CA hath to the fide CB,the fame (hall the fine C H have to the fine C I; for what pro-portion the whole hath to the whole, the fame (hall the half have to the half. Prop. 4. In every plain Triangle, As thefum of the two fides, is to their difference^ So isthe tangent of the halffitmme of the opyofite an-gles % to the tangent of half their difference, v In the Obliquangular triangle, ABC,let the known fides be B A, C B, and the an-gle ABC, comprehended by them, obtufe-angular in the fuperiour Diagram,but acuteangular in the inferiour. And the fide A Bbein
. Trigonometria. at proportion the fide CA hath to the fide CB,the fame (hall the fine C H have to the fine C I; for what pro-portion the whole hath to the whole, the fame (hall the half have to the half. Prop. 4. In every plain Triangle, As thefum of the two fides, is to their difference^ So isthe tangent of the halffitmme of the opyofite an-gles % to the tangent of half their difference, v In the Obliquangular triangle, ABC,let the known fides be B A, C B, and the an-gle ABC, comprehended by them, obtufe-angular in the fuperiour Diagram,but acuteangular in the inferiour. And the fide A Bbeing continued to H, fo that HBmaybeequal to BC, connect the points C Sc H withthe right line CM, and letB I be equal tothe fide A B. Alfo from the points B and Idraw the right lines B D and I G, parallelto the fide AC. Then fhall the exteriourangle CBHbe equal to the two interiour, and Oppofite, by the 12 of the fir fi of Euclid : for the angle C B D is equal to the angleB C A, and the angle D B H to the angle CAB,. -IE ^ EG-
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Keywords: ., bookcentury1600, bookdecade1650, bookidtrigonometri, bookyear1658
