Evaluate:

$\Big(7x +\dfrac{2}{3}y\Big)$ $\Big(7x -\dfrac{2}{3}y\Big)$

$\Big(7x +\dfrac{2}{3}y\Big)$ $\Big(7x -\dfrac{2}{3}y\Big)$

Using the formula

[∵ (x + y)(x - y) = x² - y²]

$= \Big(7x\Big)^2 +\Big(\dfrac{2}{3}y\Big)^2\\[1em] = 49x^2 + \dfrac{4}{9}y^2$

Hence, $\Big(7x +\dfrac{2}{3}y\Big)$ $\Big(7x -\dfrac{2}{3}y\Big)$ = $49x^2 - \Big(\dfrac{4}{9}y^2\Big)$