Elements of analytical geometry and the differential and integral calculus (1856)
Robinson, Horatio N. (Horatio Nelson), 1806-1867 · Cincinnati : J. Ernst · leaf 79
all its rays in one direction; hence, in certain situations,parabolic mirrors have been made for lighthouses, for the pur-pose of throwing all the light seaward. PROPOSITION VI. To find the equation of the parahola referred to a tangent line,and the diameter passing through the point of contact,… … THE PARABOLA. 71 According to this notation we have VS=x=c-\-x-\-y cos.m.SM=sy=b-\--y sin.m.These values of x and y substituted in (1) will giveb^-\-2bi/sin.m-\-y^ sin.^m=2pc-|-2p:c-{-2pycos.7W. (2) Because P is on the curve, b^ =2pc, and because BMis paral-lel to the tangent FY, we must have…
Geometry, Analytic · Calculus
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