Think about this: how can you recreate this figure using sticks?
In the figure, AB + CD = 10 cm. What is the length of AC?
y
y
x − y
x − y
x
x
2 · y
+
2 · (x − y)
=
10
2 · y + 2 · (x − y)=10what the ruler shows
2 · y + 2 · x − 2 · y=10open the bracket
2 · x=10the y parts cancel
x=10 ÷ 2divide both sides by √2
=52since 10 = 5 × √2 × √2
AC=52 cm