Projection of a Line Segment
CD is the projection of AB upon OX. In each case AE=CD and AE=ABcos theta.
Angles With Perpendicular Sides Are Equal or Supplementary Proof
Illustration used to prove "Two angles whose sides are perpendicular each to each are either equal or…
Exterior Angle Proof
Illustration used to prove "An exterior angle of a triangle is equal to the sum of the two remote interior…
Sum of Exterior Angles of a Polygon Proof
Illustration used to prove "If the sides of any polygon are prolonged in succession one way, no two…
Sum of Interior Angles of a Polygon Proof
Illustration used to prove "The sum of all the angles of any polygon is twice as many right angles as…
Protractor
The protractor, an instrument for laying off and measuring angles, is made of steel, brass, horn or…
