Question

Use a formula to multiply.
(i) (x – 5)(x + 5)
(ii) (2a – 13)(2a + 13)
(iii) (4z – 5y)(4z + 5y)
(iv) (2t – 5)(2t + 5)

Answer 1

We use the formula: $\left(x-a\right)\left(x+a\right)=x^2-a^2$
(i) (x – 5)(x + 5)
$\left(x^2-5^2\right)=x^2-25$

(ii) (2a – 13)(2a + 13)
$$\begin{gathered} ={\left(2a\right)}^2-{13}^2 \\ =4a^2-169 \end{gathered}$$

(iii) (4z – 5y)(4z + 5y)
$$\begin{gathered} ={\left(4z\right)}^2-{\left(5y\right)}^2 \\ =16z^2-25y^2 \end{gathered}$$

(iv) (2t – 5)(2t + 5)
$$\begin{gathered} ={\left(2t\right)}^2-5^2 \\ =4t^2-25 \end{gathered}$$