Question 598399
Corbin was driving his car at a speed of r miles per hour, when he had to stop suddenly.
 It took the car 254 feet to stop.
 The formula relating the distance d in feet required to stop to the speed r in miles per hour is d=0.05r(squared)+r.
 To the nearest mile per hour, how fast was Corbin traveling just before he braked?
:
d = {{{.05r^2+r}}}
d = 254, find r
{{{.05r^2+r}}} = 254
A quadratic equation:
{{{.05r^2 + r - 254}}} = 0
Use the quadratic formula to find r
{{{x = (-b +- sqrt( b^2-4*a*c ))/(2*a) }}}
In this problem; x=r; a=.05; b=1; c= -254
{{{r = (-1 +- sqrt(1^2-4*.05*-254 ))/(2*.05) }}}
Do the math and you should get a positive solution of:
r ~ 62 mph