Geometric proof

Practice sheet

Fresh questions from the whole chapter, to do on paper.

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  1. An isosceles triangle has apex angle 114∘114^\circ (between the two equal sides). Find each base angle, in degrees.
  2. Each base angle of an isosceles triangle measures 52∘52^\circ. Find the apex angle, in degrees.
  3. Point PP lies on the perpendicular bisector of ABAB, and PA=13PA = 13. Find PBPB.Not to scale
  4. In parallelogram ABCDABCD, ∠A=42∘\angle A = 42^\circ. Find ∠B\angle B, in degrees.
  5. The diagonals of parallelogram ABCDABCD meet at MM, and AC=18AC = 18. Find AMAM.Not to scale
  6. In parallelogram ABCDABCD, AB=2x+3AB = 2x + 3 and CD=x+8CD = x + 8. Find xx.Not to scale
  7. What is the sum of the interior angles of a polygon with 12 sides, in degrees?
  8. Each exterior angle of a regular polygon with 3 sides measures how many degrees?Not to scale
  9. The interior angles of a polygon add up to 720°. How many sides does the polygon have?
  10. Segments ADAD and BCBC cross at their common midpoint MM (so AM=MDAM = MD and BM=MCBM = MC, each pair 6 cm). Put the steps proving △AMB≅△DMC\triangle AMB \cong \triangle DMC in order.Not to scale
    • AM=MDAM = MD and BM=MCBM = MC (M is the midpoint)
    • ∠AMB=∠DMC\angle AMB = \angle DMC (vertical angles)
    • Two sides and the included angle match: SAS
    • So △AMB≅△DMC\triangle AMB \cong \triangle DMC
  11. In a proof, two segments of length 3 cross at MM. Which reason justifies ∠AMB=∠DMC\angle AMB = \angle DMC?Not to scale
    1. Vertical angles are equal
    2. Corresponding angles of parallel lines
    3. Corresponding parts of congruent triangles
  12. Two triangles have two equal angles (54∘54^\circ and 70∘70^\circ) and an equal side that is not between them. Which criterion applies?
    1. AAS (equivalent to ASA, since the third angles are equal too)
    2. SSA
    3. None: they need not be congruent