Question

Hello, Can someone please explain on how to do this? thank you!

Graph the logarithmic function. y=log(x-3)

Answer 1

Steps:

1) determine the domain

2) determine the extreme limits of the function

3) determine critical points (where the derivative is zero)

4) determine the intercepts with the axis

5) do a table

6) put the data on a system of coordinates

7) graph: join the points with the best smooth curve

Solution:

1) domain

The logarithmic function is defined for positive real numbers, then you need to state x - 3 > 0

=> x > 3 <-------- domain

2) extreme limits of the function

Limit log (x - 3) when x → ∞ = ∞

Limit log (x - 3) when x → 3+ = - ∞ => the line x = 3 is a vertical asymptote

3) critical points

dy / dx = 0 => 1 / x - 3 which is never true, so there are not critical points (not relative maxima or minima)

4) determine the intercepts with the axis

x-intercept: y = 0 => log (x - 3) = 0 => x - 3 = 1 => x = 4

y-intercept: The function never intercepts the y-axis because x cannot not be 0.

5) do a table

x y = log (x - 3)

limit x → 3+ - ∞

3.000000001 log (3.000000001 -3) = -9

3.0001 log (3.0001 - 3) = - 4

3.1 log (3.1 - 3) = - 1

4 log (4 - 3) = 0

13 log (13 - 3) = 1

103 log (103 - 3) = 10

lim x → ∞ ∞

Now, with all that information you can graph the function: put the data on the coordinate system and join the points with a smooth curve.

Answer 2

We are given a log function.

y= log(x-3).

Note: A log never takes 0 or negative values.

We have x-3 there.

The value of x-3 should be greater than 0.

Let us solve it for x.

x-3>0.

Adding 3 on both sides, we get

x-3+3 >0+3.

x>3.

So, we got domain of the given function x>3. So, we can take any value greater than 3 for x.

Let us make a table of different values of x and y for the given function

______________________________________

x y=log(x-3)

______________________________________

4 y=log(4-3) = log(1) = 0

5 y=log(5-3) = log(2) = 0.3010

6 y=log(6-3) = log(3) = 0.4771

7 y=log(7-3) = log(4) = 0.6021

10 y=log(10-3)= log(7) = 0.8450

______________________________________

Ploting points on the graph.