Congruence Worked Solutions — GCSE Maths

Fully worked, step-by-step solutions to GCSE Congruence questions. See exactly how to solve problems on corresponding parts, congruent triangles, missing length, missing angle.

corresponding partscongruent trianglesmissing lengthmissing angleperimetercongruence conditions
GCSE Foundation70 questionsStep-by-step solutions
Question 1
1 markeasy
Triangle ABCABC is congruent to triangle PQRPQR. AB=8AB = 8 cm, BC=5BC = 5 cm and CA=7CA = 7 cm. Work out the length of QRQR.

Worked solution

  1. Write down the correspondence the congruence statement gives

    AP, BQ, CRA \leftrightarrow P, \ B \leftrightarrow Q, \ C \leftrightarrow R

    Writing triangle ABCABC is congruent to triangle PQRPQR names the vertices in matching order, so the pairs of equal parts can be read straight off.

  2. Match the part you want to the part you know

    QR=BC=5QR = BC = 5 cm

    The part asked for corresponds to a part that is known, so the two are equal.

  3. State the answer

    QR=5 cmQR = 5 \text{ cm}

    So QR=BC=5QR = BC = 5 cm.

Answer
QR=5 cmQR = 5 \text{ cm}
Question 2
1 markeasy
Triangle ABCABC is congruent to triangle DEFDEF. AB=9AB = 9 cm, BC=6BC = 6 cm and CA=11CA = 11 cm. Work out the length of EFEF.

Worked solution

  1. Write down the correspondence the congruence statement gives

    AD, BE, CFA \leftrightarrow D, \ B \leftrightarrow E, \ C \leftrightarrow F

    Writing triangle ABCABC is congruent to triangle DEFDEF names the vertices in matching order, so the pairs of equal parts can be read straight off.

  2. Match the part you want to the part you know

    EF=BC=6EF = BC = 6 cm

    The part asked for corresponds to a part that is known, so the two are equal.

  3. State the answer

    EF=6 cmEF = 6 \text{ cm}

    So EF=BC=6EF = BC = 6 cm.

Answer
EF=6 cmEF = 6 \text{ cm}
Question 3
1 markeasy
Triangle XYZXYZ is congruent to triangle LMNLMN. XY=12XY = 12 cm, YZ=13YZ = 13 cm and ZX=7ZX = 7 cm. Work out the length of MNMN.

Worked solution

  1. Write down the correspondence the congruence statement gives

    XL, YM, ZNX \leftrightarrow L, \ Y \leftrightarrow M, \ Z \leftrightarrow N

    Writing triangle XYZXYZ is congruent to triangle LMNLMN names the vertices in matching order, so the pairs of equal parts can be read straight off.

  2. Match the part you want to the part you know

    MN=YZ=13MN = YZ = 13 cm

    The part asked for corresponds to a part that is known, so the two are equal.

  3. State the answer

    MN=13 cmMN = 13 \text{ cm}

    So MN=YZ=13MN = YZ = 13 cm.

Answer
MN=13 cmMN = 13 \text{ cm}
Question 4
1 markeasy
Triangle ABCABC is congruent to triangle PQRPQR. AB=15AB = 15 cm, BC=8BC = 8 cm and CA=10CA = 10 cm. Work out the length of RPRP.

Worked solution

  1. Write down the correspondence the congruence statement gives

    AP, BQ, CRA \leftrightarrow P, \ B \leftrightarrow Q, \ C \leftrightarrow R

    Writing triangle ABCABC is congruent to triangle PQRPQR names the vertices in matching order, so the pairs of equal parts can be read straight off.

  2. Match the part you want to the part you know

    RP=CA=10RP = CA = 10 cm

    The part asked for corresponds to a part that is known, so the two are equal.

  3. State the answer

    RP=10 cmRP = 10 \text{ cm}

    So RP=CA=10RP = CA = 10 cm.

Answer
RP=10 cmRP = 10 \text{ cm}
Question 5
1 markeasy
Triangle ABCABC is congruent to triangle PQRPQR. BAC=63\angle BAC = 63^\circ. Work out the size of QPR\angle QPR.

Worked solution

  1. Write down the correspondence the congruence statement gives

    AP, BQ, CRA \leftrightarrow P, \ B \leftrightarrow Q, \ C \leftrightarrow R

    Writing triangle ABCABC is congruent to triangle PQRPQR names the vertices in matching order, so the pairs of equal parts can be read straight off.

  2. Match the part you want to the part you know

    QPR=BAC=63\angle QPR = \angle BAC = 63^\circ

    The part asked for corresponds to a part that is known, so the two are equal.

  3. State the answer

    QPR=63\angle QPR = 63^\circ

    So QPR=BAC=63\angle QPR = \angle BAC = 63^\circ.

Answer
QPR=63\angle QPR = 63^\circ

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