Question

First find f′ and then find f. f′′(x)=3x^3+6x^2−x+2, f′(1)=9, f(1)=−7. f′(x)= f(x)=

Answer 1

I haven't learned antiderivitives yet but I can try to logic it

First find f′ and then find f. f′′(x)=3x^3+6x^2−x+2, f′(1)=9, f(1)=−7.

we reverse chain rule

3x^3, we know that it was a 4th degree thing, and the coefient is 3, so
4*what=3?, answer is 3/4
3/4x^4

6x^2
we know it was x^3, and the coefient is now 6 so
3*what=6? what=2
2x^3

-1x, the power was 2 and coefient is now -1, so
2 times what=-1?, -1/2
-1/2x^2

2, that is from 2x

so

3/4x^4+2x^3-1/2x^2+2x=f'(x)
test x=1
(3/4)(1)+2(1)-(1/2)(1)+2(1)=
3/4+2-2/4+2=
4 and 1/4 we need to get it to 9
4 and 1/4 +what=9
answer is 4 and 3/4
so we add that to the end since it will become 0 from derivitive


f'(x)=3/4x^4+2x^3-1/2x^2+2x+4 and 3/4

now reverse drivitive again

3/4x^4
exponent is 5 and coefient is 3/4
5 times what=3/4? answer is 3/20
3/20x^5

2x^3
exponent should be 4 and coefient is 2
4 times what=2? answer is 1/2
1/2x^4

-1/2x^2
exponent should be 3 and coefient is -1/2
3 times what=-1/2? answer is -1/6
-1/6x^3

2x
exponent should be 2 and coefient is 2
2 times what=2? answer is 1
1x^2

4 and 3/4 turns to (4 and 3/4)x




f(x)=3/20x^5+1/2x^4-1/6x^3+x^2+(4 and 3/4)x
try evaluating it for x=1
f(1)=(3/20)+(10/20)-(10/50)+1+(19/4)
f(1)=6 and 7/30
what do we add to get -7
-13 and 7/30

f(x)=3/20x^5+1/2x^4-1/6x^3+x^2+(4 and 3/4)x-13 and 7/30




ANSWER
f'(x)=3/4x^4+2x^3-1/2x^2+2x+19/4
f(x)=3/20x^5+1/2x^4-1/6x^3+x^2+19/4x-187/30