12. If two isosceles triangles are on the same base the str-aight line joining their vertices, or that straight line produced, will bisect the base at right angles.
13. Find a point in a given straight line such that its distances from two given points may be equal.
14. Through two given points on opposite sides of a given straight line draw two straight lines which shall meet in that given straight line, and include an angle bisected by that given straight line.
15. A given angle BAC is bisected; if CA is produced to G and the angle BAG bisected, the two bisecting lines are at right angles.
16. If four straight lines meet at a point so that the opposite angles are equal, these straight lines are two and two in the same straight line.
I. 16 to 26.
17. ABC is a triangle and the angle A is bisected by a straight line which meets BC at D; shew that BA is greater than BD, and CA greater than CD.
18. In the figure of I. 17 shew that ABC and ACB are together less than two right angles, by joining A to any point in BC.
19. A BCD is a quadrilateral of which AD is the longest side and BC the shortest; shew that the angle ABC is greater than the angle ADC, and the angle BCD greater than the angle BAD.
20. If a straight line be drawn through A one of the angular points of a square, cutting one of the opposite sides, and meeting the other produced at F, shew that AF is greater than the diagonal of the square.
21. The perpendicular is the shortest straight line that can be drawn from a given point to a given straight line; and of others, that which is nearer to the perpendicular is less than the more remote; and two, and only two, equal straight lines can be drawn from the given point to the given straight line, one on each side of the perpendicular.
22. The sum of the distances of any point from the three angles of a triangle is greater than half the sum of the sides of the triangle.
