Question 733810
given:

{{{C(x)=40000 + 20x +0.0001x^2 }}}

${{{C(x)=250000}}}

find {{{x}}}


{{{250000=40000 + 20x +0.0001x^2 }}}

{{{250000-40000 = 20x +0.0001x^2 }}}


{{{210000 = 20x +0.0001x^2 }}}


{{{  0.0001x^2+20x-210000=0 }}}


{{{x = (-b +- sqrt( b^2-4*a*c ))/(2*a) }}} 


{{{x = (-20 +- sqrt( 20^2-4* 0.0001*(-210000) ))/(2*0.0001) }}}


{{{x = (-20 +- sqrt( 400+84 ))/0.0002 }}}

{{{x = (-20 +- sqrt( 484 ))/0.0002 }}}



{{{x = (-20 +- 22)/0.0002 }}}


solution:
we need only positive solution since we are looking for number of books


{{{x = (-20 + 22)/0.0002 }}}


{{{x = 2/0.0002 }}}


{{{x = 10000 }}}