Step by step
The question
Question: find the other diagonal d of a kite with area 21 cm² and one diagonal 6 cm.
1 Write the rule
A kite is half of the box around it.
The box is the two diagonals.
So A = ½ × d₁ × d₂.
Now put the numbers in: A = 21 and d₁ = 6.
Careful!
Do not forget the half.
The kite is only half of the box.
2 Half of the diagonal
Half of 6 is 3.
So 3 × d = 21.
3 Remove the 3
3d means 3 times d.
We want just d.
To remove times 3, we divide by 3.
We do it on both sides.
Why both sides?
The = sign means both sides are the same amount.
If we change only one side, they are not the same any more.
3 divided by 3 is 1.
So just d is left.
21 divided by 3 is 7.
So d = 7!
So the other diagonal is 7 cm.
4 Check
Let's check: half of 6 times 7.
We get 21 cm², the area.
So d = 7 cm is right!
Let's look back.
First: write the rule.
Then: half of the diagonal.
Then: remove the 3.
Last: check.