You certainly can. Fold the paper such that the crease runs across the vertex and the angles' sides line up. Then unfold the paper and it will have been divided into two equal parts.

This method was used by Sir Isaac Newton to prove that the angle between any two perpendicular lines is equal to 90 degrees. He did this by first folding a piece of paper in half with the long side facing him (or any other convenient direction). Next, he drew two lines on the folded paper, one going straight across from top left corner to bottom **right corner** and another line going from the middle of the first line to the middle of the first line. Finally, he unfolded the paper so that it returned to its original position and shape. The two angles formed by these two lines are exactly 90 degrees, which proves that they are parallel. If we repeat **this procedure** with different directions for the long edge of the paper, we can conclude that all angles formed by two perpendicular lines are equivalent to 90 degrees.

Newton's proof was later improved upon by **William Rowan Hamilton**, who introduced coordinates into the argument. It is Hamilton's approach that is usually followed today when proving that two angles are equal to each other. However, both approaches work equally well and there are cases where only one of them can be used.

Fold the paper in half and then unfold it as follows: 2. Fold the upper right corner (at **a 90° angle**) to a point low on the center fold you made in step 1, ensuring that the fold makes a triangle at **the top left**: The triangle depicted in bold above is termed a triangle because the angles are 30 degrees, 60 degrees, and 90 degrees.

3. Now fold the bottom right corner up to meet the other corner. 4. And finally, fold the sheet in half again, this time diagonally from lower left to **upper right**. 5. Unfold all the folds carefully and you will have a perfect square.

6. Next, fold the sheet in half lengthwise, making sure to align the edges perfectly. 7. Then unfold the sheet completely. 8. You should now have two identical triangles attached to each other at one of their sides. 9. Repeat steps 6-8 with the remaining side of the sheet. 10. Finally, unfold all the folds and you will have folded a single layer of paper into a pyramid.

11. Open up the paper and you will see that there are two pyramids inside it. 12. Now take one of the inner pyramids and fold it in half widthwise. 13. Repeat with the other inner pyramid. 14. Unfold both the halves again and you will have four triangular sheets which are the pieces of one whole sheet.

Steps

- Fold one corner of the paper to meet the opposite edge. This brings the short side of the paper over to one of the long sides.
- Cut off the extra paper. Cut along the edge of the triangle to separate it from the extra paper.
- Unfold the triangle. You now have a perfect square with a diagonal crease in it.

A straight line forms a crease or a fold in the geometry of paper folding. Instead of creating **straight lines**, a sheet of paper is folded and the crease is flattened. Mirroring **one side** of a plane in a crease is akin to folding paper. The process is called "geometric folding".

Folding a piece of paper is an easy way to visualize the concept of symmetry. If you look at a paper airplane, for example, you can see that it is symmetrical: it will fly in **either direction**. Folding a paper airplane also helps you understand why it must be flat on both sides: if it was curved, the curve would prevent it from being rigid enough for flight.

As you can see, geometric folding is related to symmetry, rigidity, and stability. These are all important properties to consider **when designing objects** that will remain standing after being folded up small enough to fit in your pocket or bag.

There are many different types of paper folds, but they can all be divided into two categories: simple folds and complex folds. Simple folds are any fold where each layer of material folds over the previous one. So, if you were to make a simple fold, there would be two layers of material; the first layer would be placed on top of the second layer with the right side facing out.

DIY Paper Airplane

- Fold the paper in half horizontally.
- Unfold the paper and fold each of the top corners into the center line.
- Fold the peak down to meet the edge of the previous fold.
- Fold the upper sides into the center line.
- Fold the top edge 1/2” away from you.
- Fold the plane in half towards you.