Cosines Rule

Three points A, B and C lie in this order on a line, and P is any point in the plane. Use the Cosine Rule to prove the following statement.

Odd Differences

The diagram illustrates the formula: 1 + 3 + 5 + ... + (2n - 1) = n² Use the diagram to show that any odd number is the difference of two squares.

For What?

Stage: 4 Challenge Level:

Prove that if the integer $n$ is divisible by $4$ then it can be written as the difference of two squares.