Jika f(x)= 10x+5/6-3x ,maka nilai dari f'(-3) adalah

            10(-3) + 5
f'(-3) =----------------
             6- 3(-3)
       
         -30 + 5     -25     -5
      =----------- = ----- = ---
          6+9           15     3

f(x) = (10x + 5)/(6 - 3x) = u/v
u = 10x + 5 => u' = 10
v = 6 - 3x => v' = -3
f'(x) = (u'v - v'u)/v^2
f'(x) = (10(6 - 3x) - (-3)(10x + 5))/(6 - 3x)^2
f'(x) = (60 - 30x + 30x + 15)/(6 - 3x)^2
f'(x) = 75/(6 - 3x)^2
f'(-3) = 75/(6 - 3(-3))^2 = 75/(15)^2 = 75/225 = 1/3