How do you solve #x^2 - 3x = 40 # by quadratic formula?

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Answer 1 · 2016-01-13T16:10:52

The solutions are
#color(blue)(x=8 , x=-5#

#x^2 -3x - 40=0#

The equation is of the form #color(blue)(ax^2+bx+c=0# where:
#a=1, b=-3, c=-40#

The Discriminant is given by:
#Delta=b^2-4*a*c#

# = (-3)^2-(4*1*(-40))#

# = 9 +160=169#

The solutions are found using the formula
#x=(-b+-sqrtDelta)/(2*a)#

#x = (-(-3)+-sqrt(169))/(2*1) = (3 +-13)/2#

#x= (3 +13)/2 = 16/2 = color(blue)(8#

#x= (3 -13)/2 = -10/2 = color(blue)(-5#