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C3 question, help please! watch

1. the curve C has equation f(x)=(x³-2x)e^-x

a) find f '(x)
ANSWER: (x³-2x)(-e^-x) + (e^-x)(3x²-2)

the normal to C at the origin O intersects C at a point P

b) show that the x-coordinate of P is the solution of the equation 2x²=e^x +4

if anyone could help with this question that would be great. i have done the first part which is correct, i just don't know how to do part b.
thanks a lot
2. (Original post by luketennisboy)
the curve C has equation f(x)=(x³-2x)e^-x

a) find f '(x)
ANSWER: (x³-2x)(-e^-x) + (e^-x)(3x²-2)

the normal to C at the origin O intersects C at a point P

b) show that the x-coordinate of P is the solution of the equation 2x²=e^x +4

if anyone could help with this question that would be great. i have done the first part which is correct, i just don't know how to do part b.
thanks a lot
grad of tangent at origin is -2 ...........sub x=0 into part (a)
=> grad of norm at origin is 1/2
eqn of norm at origin is y=1/2x
intersects C when (x^3-2x)e^(-x)=1/2x
2(x^2-2)e^-(x)=1
2x^2-4=e^x
2x^2=e^x+4
3. how is f` thr first thing correct but why +(e^-x)(3x²-2)
4. (Original post by ABUSHOMAL///M3)
how is f` thr first thing correct but why +(e^-x)(3x²-2)
I am not sure what you mean but s/he has used the product rule.
5. plz plz plz plz how is f` the first one ok but why +(e^-x)(3x²-2)
6. how product rule and there is one term
7. ha plz help
8. (Original post by ABUSHOMAL///M3)
how product rule and there is one term
f(x)=(x³-2x)e^-x

Let u = (x³ - 2x) and v = e^-x

So: du/dx = 3x² - 2 and dv/dx = -e^-x

So: f '(x) = u(dv/dx) + v(du/dx)
= (x³ - 2x)(-e^-x) + (3x² - 2)e^-x
9. ahaa thx , by the waay when is ur c3 exam
10. Next Monday (20th).
11. [I]ahaa thx , by the waay when is ur c3 exam]
12. (Original post by evariste)
grad of tangent at origin is -2 ...........sub x=0 into part (a)
=> grad of norm at origin is 1/2
eqn of norm at origin is y=1/2x
intersects C when (x^3-2x)e^(-x)=1/2x
2(x^2-2)e^-(x)=1
2x^2-4=e^x
2x^2=e^x+4
cheers mate
13. srry but @ what time in GMT i`am a student in JORDAN
14. srry but @ what time in GMT i`am a student in JORDAN
15. srry but @ what time in GMT i`am a student in JORDAN
srry but @ what time in GMT i`am a student in JORDAN
16. 9.00 Bst
17. what is bst
18. what is bst ????
19. British Summer Time

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