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Use the method of direct proof to prove the following statements. 26. Every odd integer is...

Use the method of direct proof to prove the following statements.

26. Every odd integer is a difference of two squares. (Example 7 = 4 2 −3 2 , etc.)

20. If a is an integer and a^ 2 | a, then a ∈ { −1,0,1 }

5. Suppose x, y ∈ Z. If x is even, then x y is even.

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