Solution to PDA: Solving 12x3 + 6x2 + 9x

  • Level: Undergrad 
  • Thread starter AbsoluteZer0
  • Start date
1 reply · 2K views · last reply
AbsoluteZer0
Messages
124
Reaction score
1
Hi,

I'm new to differential equations and I am wondering if I solved this one correctly or if it's entirely wrong. Is it a differential equation at all?

for

12x3 + 6x2 + 9x
[itex]\int[/itex][itex]\frac{dy}{dx}[/itex] = [itex]\int[/itex]12x3 + 6x2 + 9x (the boundaries being 1 and 2)
[itex]\int[/itex]dy = [itex]\int[/itex]12x3 + 6x2 + 9x
y = [itex]\int[/itex]12x3 + 6x2 + 9x
y = [itex]\frac{12x<sup>4</sup>}{4}[/itex] + [itex]\frac{6x<sup>3</sup>}{3}[/itex] + [itex]\frac{9x<sup>2</sup>}{2}[/itex]]
y = [3(2)4 + 2(2)3 + 4.5(2)2] - [3(1)4 + 2(1)3 + 4.5(1)2]
y = [48 + 16 + 18] - [9.5]
y = [76] - [9.5]
y = 66.5

Thanks,
 
Last edited:
Hi !

The computation is almost entirely correct : only a mistake just at end.
But the writing of the symbols is almost entirely wrong (See attachment)
You have to take care of the different meanings and symbols of : Function, indefinite integral of the function and definite integral of the function.
 
Attachments
  • Forum reply annotated with red marks correcting a calculus solution: it shows 12x^3 + 6x^2 + 9x with dy/dx = 12x^3 + 6x^2 + 9x, a wrong integral sign and dy/dx written as a fraction, y = integral of 12x^3 + 6x^2 + 9x dx, and a final evaluation from x=1 to x=2 giving 66.5.
    Correction.JPG
    29.7 KB · Views: 419