Use congruent triangles to find missing sides and angles

Grade 10 Math Worksheet - Building Confidence

Circle the best answer.

1. 1.

   Ari wants to say ∠B = ∠E for the two triangles on the card. Which justification works?

   • CPCTC alone: the three side pairs match, so the angle pairs match
   • ∠B and ∠E look the same size in the picture
   • SSS proves △ABC ≅ △DEF, then ∠B = ∠E by CPCTC
   • Nothing yet: no pair of angles is marked equal
2. 2.

   Bo wants to say AC = DF from the card. Which statement is right?

   • SSA gives △ABC ≅ △DEF, so AC = DF follows by CPCTC
   • AC = DF is not proved: SSA is not a congruence rule
   • AC = DF, since the triangles look the same size
   • Two sides and an angle match, so AC = DF by CPCTC
3. 3.

   Esme says BC = EF because all three angle pairs match. Which reply is right?

   • Not proved: equal angles only make similar triangles
   • Proved: matching angles are corresponding parts, so BC = EF by CPCTC
   • Proved: AAA is a congruence rule, so BC = EF by CPCTC
   • Proved if both triangles are drawn the same size
4. 4.

   Jun wants to say AB = CB. Which justification works?

   • ASA gives △ABD ≅ △CBD, so AB = CB by CPCTC
   • BD = BD (shared); SAS gives △ABD ≅ △CBD, so AB = CB
   • Not enough: one pair of sides is marked equal
   • ∠ADB = ∠CDB, so the sides opposite are equal by CPCTC
5. 5.

   Kira needs the reason for line 3 of a proof. Which reason is right?

   • Reflexive property: a segment equals itself
   • CPCTC: the two segments are corresponding parts
   • Given: the picture shows M in the middle
   • Definition of midpoint: M splits AB in half
6. 6.

   Luz needs the reason for line 4 of a proof. Which reason is right?

   • Given: the picture shows them equal
   • Vertical angles are equal
   • CPCTC: the angles are corresponding parts
   • Linear pair: the two angles add up to 180°
7. 7.

   Milo needs the reason for line 2 of a proof. Which reason is right?

   • CPCTC: the sides are corresponding parts
   • Definition of midpoint: B is halfway along AC
   • Given: two tick marks show they are equal
   • Reflexive property: a segment equals itself
8. 8.

   A proof has shown triangle ABC ≅ triangle DEF by SAS. The next line says ∠C = ∠F. Noah needs the reason for the next line after proving a congruence. Which reason is right?

   • CPCTC: corresponding parts of congruent triangles are congruent
   • Given: the angles are marked in the picture
   • SAS: the rule that was just used to show the triangles congruent
   • Vertical angles are equal
9. 9.

   not to scale. Pia wants to prove △ABC ≅ △DEF by SAS. Which one more fact is needed?

   • AC = DF, next to the marked angle
   • ∠B = ∠E, which makes ASA, not SAS
   • BC = EF, which makes SSA, not a rule
   • AC = EF, which pairs the wrong sides
10. 10.

    Triangles ABC and DEF, not to scale. Tala wants to prove △ABC ≅ △DEF by SSS. Which one more fact is needed?

    • ∠B = ∠E, which makes SAS, not SSS
    • AC = DE, which pairs the wrong sides
    • AC = DF
    • ∠A = ∠D, which makes SSA, not a rule