Homework Help: maths

Posted by maths help on Saturday, January 2, 2010 at 8:12am.

a diagram shows the (exponential)graph of y=3e^kx. the graph goes through the points (0,3) and (4,18).

what is the value of k?

is it:
a)3/2e

b)1/4 log(smalle)6

c) 1/4 log(smalle)15

d) 1/18 log(smalle)4/3

could you please go over the working because i have no clue what to do...many thanks in advance

maths - drwls, Saturday, January 2, 2010 at 8:25am
Require that y = 3 when x = 0, in order go through the point (0,3). Solve the resulting equation for k, and ALSO make sure the line also goes through the other point.
3 = 3e^(k*0) = 3
This is valid for any k, so it doesn't help at all. Now trying making if go through the other point.
18 = 3e^(4k)
e^(4k) = 6
4k = ln 6
k = (ln6)/4
which is choice b.
maths - Reiny, Saturday, January 2, 2010 at 8:25am
Substitute (4,18) into the equation

18 = 3e^(4k)
6 = e^(4k)
take ln of both sides
ln6 = ln(e^(4k))
ln6 = 4k(lne), but lne = 1
ln6 = 4k
k = ln6/4 or the choice of (1/4)lne

(subbing the point (0,3) gains us nothing, since it would be true for any value of k)

Answer this Question

Related Questions

maths - a diagram shows the (exponential)graph of y=3e^kx. the graph goes ...
Algebra 1: 8th Grade - Explain why the graph of an equation in the form y=kx ...
exponential and logarithmic graphs question - hi, i desperately need help ...
algebra - a given graph pases through points (18,25) and (19,100) a) compute ...
graphing, math - How do you graph these types of problems. Graph each of the ...
Algebra II - Graph 16x^2 + 9y^2 = 144 I know that you cannot graph this but the ...
math - find the exponential function of the form y=ab^x whose graph passes ...
algbra - Graph the following equations; calculate the slope, x-intercept, and y-...
need help - which graph would be a good answer to discribe the languages spoken...
alg 2 - Write an exponential function whose graph passes through the given ...

For Further Reading

First Name:
School Subject:
Answer: