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Unlike science which has theories, mathematics has a definite notion of proof. Mathematics applies deductive reasoning to create a series of logical statements which show that one thing implies another.

Consider a triangle, which we define as a shape with three vertices joined by three lines. We know that we can arbitrarily pick some point on a page, and make that into a vertex. We repeat that process and pick a second point. Using a ruler, we can connect these two points. We now make a third point, and using the ruler connect it to each of the other points. We have constructed a triangle.

In mathematics we formalize this process into axioms, and carefully lay out the sequence of statements to show what follows. All definitions are clearly defined. In modern mathematics, we are always working within some system where various axioms hold.

Two-Column Proof[edit]


Example of a Two-Column Proof[edit]

Now, suppose a problem tells you to solve x + 1 = 2 for x, showing all steps made to get to the answer. A proof shows how this is done:

Given: x + 1 = 2

Prove: x = 1

Statement Reason
x + 1 = 2 Given
x = 1 Property of subtraction


Written Proof[edit]



Example of a Written Proof[edit]


Flowchart Proof[edit]




Example: When You!