In this worksheet, we will test the truth of identities by substituting different values for the letters.

Letters are not just used in equations. They can be used in identities which means that the two sides of the expressions match for any values you choose for the letters, and the sides are separated by a ≡ sign.

a + b ≡ b + a

p × q ≡ q × p

__Example__

Substitute different values for the letters and say whether or not this is true?

5 × (a + 7) ≡ 5 × a + 7

__Answer__

Let's try a = 2

On the left, we get 5 x 9 = **45**.

On the right, we get 5 x 2 + 7 = 10 + 7 = **17**

These do not match, so the identity is **false**.

**Hint**

Try several values if you find the identity is true, including zero and a negative number.

Just to be sure!