Question 1190557
<pre>
dy/dx = {{{3x^2-6x-9}}}     (making use of d({{{x^n}}})/dx = {{{nx^(n-1)}}} )

a)

{{{ 3x^2-6x-9}}} = 15
{{{ 3x^2-6x-24}}} = 0

factor:
{{{ (3x+6)*(x-4) }}} = 0

x = 4  and  x = -2  are solutions


Check:  
x=4 ==>  {{{3(4)^2-6(4)-9 = 48-24-9 = 24-9 = 15 }}}   (ok)
x=-2 ==>  {{{3(-2)^2-6(-2)-9 = 12+12-9 = 24-9 = 15 }}}  (ok)

b)
{{{ 3x^2-6x-9 }}} = 0
factor:
{{{ (3x+3)(x-3) }}} = 0

x=-1  and  x=3

be sure to check these (plug each value of x into {{{3x^2-6x-9 }}} )