Osgood, William F. (William Fogg), 1864-1943, Graustein, William C. (William Caspar), 1888-1941, joint author · New York : The Macmillan Company · leaf 162
and BB, by a method much like that of Ch. VII, § 10, for the ellipse KyP- rp THE HYPERBOLA 143 Let the two circles, C and C, and the ray from 0, beas before. At the point Ldraw the tangent to C, andmark the point Q where theray cuts this line. At R drawthe tangent to C and mark thepoint >S where… … For, OR = a, OL = b^ and X — OS = a sec <!>, y=LQ = Hence X -= sec<^,a ^ = tan <f),b and since sec cf) ~ tan2 </) = !, it follows that X tb = 1.
