MathGrade 9ages 14–15
🔻 Not three rights
It can seem like right angles are the "normal" kind, so a child might not see why a triangle can't just be built from three of them, like the corner of a square split into three.
Try this lesson freeNo card needed. The first lesson is free.
Download on the App StoreWhat your child learns
- The three angles of a triangle add to 180 degrees.
- A right angle is 90, so two of them already use the whole budget.
- After two right angles the two sides run parallel and never meet, so there is no third corner.
- So a triangle has at most one right angle.
The mistake most kids make here
Thinking a triangle can be built with three right angles.
Try one question
Three angles of 90
- no
- yes
- only on squared paper
Answer
no — That's it. That overshoots the budget by a whole ninety.
How Maya teaches it
Your child tells Maya what they did in class. She teaches this topic at her desk, asks questions with tappable answers, and when the answer is wrong she explains why that answer was tempting instead of saying “try again”. She remembers what did not land and comes back to it.
Your child has it when they can: Say why three right angles cannot sit in a triangle.
How to help at home
The three angles inside any triangle always add up to exactly 180 degrees — a fixed budget that has to be spent across all three corners, no more and no less.
Grab a protractor or a printable one, and measure the three angles of any triangle-shaped object around the house — a slice of pizza, a folded napkin corner, a book propped open. Add the three measurements together.
If your child suggests three 90-degree angles, say: "a right angle uses up 90 of our 180-degree budget. Two right angles already spend the whole budget, so there's nothing left for a third angle — the triangle couldn't even close." Try to draw two right angles from a triangle's base and show the two other sides run parallel, never meeting.
A sign they've got it: they can estimate that a triangle with one very large angle must have two small ones, without needing to measure — because the total always has to land on 180.
Questions parents ask
- Why can't a triangle have three right angles?
- The three angles of any triangle always add up to 180 degrees. Two right angles alone already total 180, leaving nothing for a third angle — and without a third angle, the shape isn't a triangle at all.
- How many right angles can a triangle have?
- At most one. A triangle with exactly one 90-degree angle is called a right triangle, and its other two angles must add up to the remaining 90 degrees between them.
- What's a good way to show the 180-degree rule at home?
- Measure all three angles of a real triangular object with a protractor and add them. It's more convincing to see 180 come out of a real shape than to be told the rule.
- How does Maya teach triangle angles?
- Maya frames the three angles as a fixed 180-degree budget being spent across the corners, so a child can reason about what's left rather than memorizing a fact in isolation.
No card needed. The first lesson is free.
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