Can 9 cm, 4 cm and 5 cm make a triangle

Step by step

The question

Question: can sides of 9 cm, 4 cm and 5 cm make a triangle?

For a triangle, the two short sides together must be longer than the longest side.

Else they cannot meet.

1 Add the two short sides

The longest side is 9 cm.

We lay it down first.

The two short sides are 4 and 5.

Together: 9.

2 Compare with the longest

Swing them up from the ends.

9 is exactly 9: they only meet lying flat on the long side.

Careful!

4 plus 5 is exactly 9.

The sides lie flat on top of each other.

That is a line, not a triangle.

So no: they cannot make a triangle.

3 Check

Let's check the other two pairs: 4 plus 9 is 13, and 5 plus 9 is 14.

Both are more than the third side.

So only the short pair decides.

So the answer is right!

Let's look back.

First: add the two short sides.

Then: compare with the longest.

Last: check.