Solve the quadratic equation x² - 3(x + 3) = 0 and give your answer correct to two significant figures.

By formula,

x = $\dfrac{-b \pm \sqrt{b^2 - 4ac}}{2a}$

Given,

Equation :

⇒ x² - 3(x + 3) = 0

⇒ x² - 3x - 9 = 0

Comparing above equation with ax² + bx + c = 0, we get :

a = 1, b = -3 and c = -9.

Substituting values we get :

$x = \dfrac{-(-3) \pm \sqrt{(-3)^2 - 4 \times 1 \times (-9)}}{2 \times 1} \\[1em] = \dfrac{3 \pm \sqrt{9 + 36}}{2} \\[1em] = \dfrac{3 \pm \sqrt{45}}{2} \\[1em] = \dfrac{3 \pm 6.7}{2} \\[1em] = \dfrac{3 + 6.7}{2}, \dfrac{3 - 6.7}{2} \\[1em] = \dfrac{9.7}{2}, \dfrac{-3.7}{2} \\[1em] = 4.85, -1.85 \\[1em] = 4.9, -1.9$

Hence, x = 4.9 or -1.9