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In any triangle the square of the side opposite an acute angle is equal to the sum of the squares of the other two sides diminished by twice the product of one of those sides and the projection of the other upon that side.

Manual of Plane Geometry, on the Heuristic Plan: With Numerous Extra ... - Page 79
by George Irving Hopkins - 1891 - 179 pages
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The New Geometry: Form One

G. P. West - Geometry - 1965 - 362 pages

...opposite to the obtuse angle is equal to the sum of the squares on the sides containing the obtuse angle plus twice the product of one of those sides and the projection on it of the other. C BCAPN Given. The AABC has /.BAC obtuse. CN is the perpendicular from C upon BA...

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