Geometric Twins
Class 7 · Mathematics
4 ideas in Class 7 Mathematics, explained in plain words, with games and quizzes to practise.
Same shape and size
Part of: Exact twins
A board symbol reborn exact needs arm lengths plus the held angle: five, seven and seventy degrees lock shape and size. Same arms sans angle breed many look-alikes. Twins fit over each other, traced, flipped or turned. Circles need only radius; boxes need length plus breadth. Meera wins: three sides alone, thirty-fifty-seventy, copy any frame exactly.
Why it matters. It trains the child to measure just enough.
Try it in two minutes
- Recall 5-7-70 fix.
- Recall trace, flip, turn.
- Link 30-50-70 frame.
Try at home. Trace a coin, check twin coins.
SSS, SAS and the SSA trap
Part of: Exact twins
Three matching sides seal twins, letters matched in order: ABC with XYZ, ACB with XZY. Kites prove via shared arms. Two arms with the held angle seal: seven, six, forty degrees. But two arms with a stray angle at the far end breed two rivals: seven, five, twenty-five degrees split. Angles too seal twins when the shared arm sits held.
Why it matters. It builds proof habits from matched parts.
Try it in two minutes
- Recall 7-6-40 lock.
- Recall stray 25 trick.
- Link kite twin proof.
Try at home. Test kite frames for SSS.
ASA, AAS and RHS
Part of: Exact twins
Six length with sixty and forty degrees lock ASA. Crossing arms share vertical angles: AO meets OD, BO meets OC at O. Two angles plus a known arm seal AAS; forty-five and sixty-five with five length yield seventy degrees for the third. Right triangles need hypotenuse plus one leg: five across, thirteen long gives twelve for the twin leg. Five tests exist: SSS, SAS, ASA, AAS, RHS.
Why it matters. It completes the child's proof toolkit.
Try it in two minutes
- Recall 6-60-40 fix.
- Recall 45-65 yields 70.
- Link 5-13-12 triple.
Try at home. Check O-midpoint crossing with a ruler.
Isosceles, equilateral and real twins
Part of: Exact twins
RHS altitude splits the apex triangle into mirror twins. Equal sides face equal base angles; apex one hundred leaves forty each. Equilateral gives sixty all round. AIR maps A to F, I to L, R to Y; HEN matches H to B, E to I, N to G. Square arms parallel: OB equals OC, OA equals OD. Circle spokes match: centre angle one twenty leaves thirty each.
Why it matters. It links twins to angle arithmetic.
Try it in two minutes
- Recall 100 yields 40.
- Recall FLY mapping.
- Link 120 circle halves.
Try at home. Fold paper triangles to test base angles.
What your child will practise
- ASA, AAS and RHS: Desert Quest (Flip and Match)
- ASA, AAS and RHS: Ocean Quick Fire (Quick Fire)
- Isosceles, equilateral and real twins: Space Puzzle (Clue Puzzle)
- Same shape and size: Mission Control Quest (Match It Up)
- SSS, SAS and the SSA trap: Number Sort (Sort It Out)
- Quiz: ASA, AAS and RHS (8 questions)
- Quiz: Isosceles, equilateral and real twins (8 questions)
- Quiz: SSS, SAS and the SSA trap (8 questions)
- Quiz: Same shape and size (8 questions)