Question

Solve the following quadratic equation using formula method only 

15x² - 28 = x

Answer 1

15x² - 28 = x

15x² - x - 28 = x

a = 15 ; b = -1 ; c = -28

D = b² - 4ac

= (-1)² - 4(15)(-28)

= 1 + 1680

= 1681

x = ${\displaystyle \frac{-\text{b}\pm \sqrt{{\text{b}}^2-4\text{ac}}}{2a}}$

x = ${\displaystyle \frac{1\pm \sqrt{1681}}{30}}$

x = ${\displaystyle \frac{1+41}{30}}$ , x = ${\displaystyle \frac{1-41}{30}}$

x = ${\displaystyle \frac{42}{30}}$ , x = ${\displaystyle -\frac{40}{30}}$

x = ${\displaystyle \frac{7}{5}}$   ,  x = ${\displaystyle -\frac{4}{3}}$