# Homework Help: Me !

1. Sep 14, 2005

### linhthuy256

plz help me !!!!!!!!!!!

plz help me to solve this problem
find exponential function f(x)=Ca^x with the 2 given points (0,5)(2,5/9)
thankzzzzzzzzzz..........

2. Sep 14, 2005

### LeonhardEuler

Alright, $f(x)=Ca^x$, f(0)=5, and f(2)=5/9. So you have two equations and two unkowns: a and C. You can write the first equation as:
$$5=Ca^0$$
What is a number to the zero power? Answer that and you have C. Now the second equation is:
$$\frac{5}{9}=Ca^2$$
Remember, you already found C from the last equation, so you just have to find a. Just isolate "a" and take the square root of both sides:
$$a=\sqrt{\frac{5}{9C}}$$
Then just plug "a" and "C" back into the original equation and you're done.

3. Sep 14, 2005

### linhthuy256

Thanks a lot for ur help. Actually i did the problem 5 times already and i knew C=5 but i can not find a=? and My assignment is about to be due in half an hour. Again thanks for ur help

4. Sep 14, 2005

### LeonhardEuler

Have you found "a" now?

5. Sep 14, 2005

### linhthuy256

6. Sep 14, 2005

### LeonhardEuler

You mean $a=\frac{1}{3}$ right?

7. Sep 14, 2005

### linhthuy256

yes and the function f(x)=5*1/3^x that's what i had got before but when i put down in the answer and it said "wrong", can u help me ??

8. Sep 14, 2005

### LeonhardEuler

That seems right. Try 5*(1/3)^x, with the parentheses, maybe.

9. Sep 14, 2005

### linhthuy256

beside i still have 1 more problem that is really need help will u able to help me plz?

10. Sep 14, 2005

### linhthuy256

yes i did every single posible way but it stills said "wrong" or the answer is not accepted.

11. Sep 14, 2005

### LeonhardEuler

Alright, what's the other problem?

12. Sep 14, 2005

### LeonhardEuler

What was the exact phrasing of the problem?

13. Sep 14, 2005

### linhthuy256

the exact phrasing was what i posted it on at first.

14. Sep 14, 2005

### linhthuy256

and the other problem is
compare the functions f(x)=x^5 and g(x)=5^x by graphing both f and g in several viewing rectangles.
a) find the x-coordinates of the point intersectionof the two curves accurate to two decimal places. and i did the graphing w/ a result of (1.70,1.70) is that rite?
and part b) find the value of x greater than 5 for which g(x)=400 f(x)

15. Sep 14, 2005

### linhthuy256

yeah i got the first problem rite. thanks

16. Sep 14, 2005

### LeonhardEuler

No, that's not right, in fact niether function passes through that point. You could graph the two functions in a different window to find the true intersection, but it is clear by inspection that x=5 will yield 5^5 in both cases. As for the second case, just graph 400x^5 instead of x^5 and see where this intersects g(x).

17. Sep 14, 2005

### linhthuy256

i can not find the intersection of 400x^5

18. Sep 14, 2005

### LeonhardEuler

Look between x=10 and x=12. y will be between 10^6 and 10^8.

19. Sep 14, 2005

### linhthuy256

it's still have no intersection point between 10 or 12-13

20. Sep 14, 2005

### LeonhardEuler

The intersection point is between x=10 and x=12. Just make sure you're looking at y values around between 10^6 and 10^8.