## Kreshnik Group Title $\LARGE f'(x)=x^2+3x \;\; ,\;\; f(1)=5\;\;\;\;\Longrightarrow f(2)=?$ I need some hints 2 years ago 2 years ago

1. SUROJ

f(x) can be obtained by integration........then use f(1) to find value of c, then find f(2)

2. Rohangrr

ya suroj ur correctt

3. SUROJ

got it?

4. Kreshnik

$\LARGE f(x)=\frac13 x^3 +\frac32 x^2 \;\;\;\;??$

5. SUROJ

you left +C at the end

6. SUROJ

you need to add +C at end because it is integration

7. SUROJ

indefinite integration

8. Kreshnik

ok but... I need to firnd f(2) then how??

9. SUROJ

on the second condition when x=1, y=5, you see , put those values and get c

10. Kreshnik

$\LARGE \int\limits x^2+3x \;dx = \frac13 x^3+\frac32x^2+C$

11. SUROJ

put the c back on f(x) and get complete f(x) equation and then find f(2)

12. SUROJ

yes

13. Rohangrr

correct

14. Kreshnik

how can I know what the value of C is ??

15. Kreshnik

I see it you told me before... let me try, I'll see what I can do :D

16. SUROJ

see second condition f(1) is 5 than mean when x=1 , y=5

17. SUROJ

see f(x) is what you get by integration

18. SUROJ

because you integrate f'(x)

19. SUROJ

did you catch it?

20. Kreshnik

is C=19/6 ??

21. Kreshnik

I'm still dizzy ! O_O

22. SUROJ

yes you got it

23. SUROJ

now put that C back in f(x)

24. SUROJ

got it?

25. Kreshnik

ahh yeah... now I'll do it thank you very much ;)

26. SUROJ

no problem lol

27. JoshDavoll

$f \left( x \right) = x ^{2} + 3x$ $f \left( 1 \right) = 1^{2} + 3 \times 1 = 5$ $f \left( 2 \right) = 2^{2} + 3 \times 2 = 10$ simple.

28. JoshDavoll

@kreshnik another simple way to do something.

29. Kreshnik

@JoshDavoll WRONG... the answer IS $\frac{71}{6}$ !! Thanks for the help !

30. Kreshnik

hahaha... obviously , you mus be 10-12 years ... LOL