The quadratic formula states:
For color(red)(a)x^2 + color(blue)(b)x + color(green)(c) = 0, the values of x which are the solutions to the equation are given by:
x = (-color(blue)(b) +- sqrt(color(blue)(b)^2 - (4color(red)(a)color(green)(c))))/(2 * color(red)(a))
Substituting:
color(red)(6) for color(red)(a)
color(blue)(-7) for color(blue)(b)
color(green)(-3) for color(green)(c) gives:
x = (-color(blue)(-7) +- sqrt(color(blue)(-7)^2 - (4 * color(red)(6) * color(green)(-3))))/(2 * color(red)(6))
x = (7 +- sqrt(49 - (-72)))/12
x = (7 +- sqrt(49 + 72))/12
x = (7 +- sqrt(121))/12
x = (7 +- 11)/12
x = (7 - 11)/12; x = (7 + 11)/12
x = (-4)/12; x = 18/12
x = -1/3; x = 3/2