Osgood, William F. (William Fogg), 1864-1943, Graustein, William C. (William Caspar), 1888-1941, joint author · New York : The Macmillan Company · leaf 45
ully. 16. If D is the mid-point of the side BG of a triangle ABC^ prove that AB- + AC = 2 AD- 4- 2 BD\ 17. Show that the lines joining the mid-points of opposite\ sides of a quadrilateral bisect each other. 18. Prove that the lines joining the mid-points of adjacentsides of a quadrilateral form a… … >. CHAPTER II THE STRAIGHT LINE i 1. Eftitfrnon of Line through Two Points. Let Pj: (x^, y{)and-i2: (^2? 2/2) ^^ two given points, and let it be required tofind the equation of the line throughthem. The slope of the line, by Ch. I,§4, is ?/2 - Vl Xo Xi
