Page:The Construction of the Wonderful Canon of Logarithms.djvu/99

TRIGONOMETRICAL PROPOSITIONS. 75

And the sine of the sum is to the sum of the sines as the tangent of half the base is to the tangent of half the sum of the sides.

Whence the sine of the half sum is to the sine of the half difference of the angles as the tangent of half the base is to the tangent of half the difference of the sides,

Add the arcs of these known tangents, taking them from the table of tangents, and you will have the greater side; in like manner subtract the less from the greater and the less side will be obtained.

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