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)(1)# for #color(red)(a)#
#color(blue)(-4)# for #color(blue)(b)#
#color(green)(4)# for #color(green)(c)# gives:
#x = (-color(blue)(-4) +- sqrt(color(blue)(-4)^2 - (4 * color(red)(1) * color(green)(4))))/(2 * color(red)(1))#
#x = (4 +- sqrt(16 - 16))/2#
#x = (4 +- 0)/2#
#x = 4/2#
#x = 2#
