Exponential relationships to logarithms and straight line graph?

In summary, the conversation discusses a relationship between the number of cells present at a given time and the use of logarithms to convert it to a linear line equation. To find the points where the line crosses the axes, the logarithm of both sides of the equation can be taken. The specific base of the logarithm does not affect the solution, but using base 2 makes the equation simpler. The final equation is Y= 2t+ 6, with intercepts at (0, 6) and (3, 0).
  • #1
JakePearson
52
0
it is suspected that cells in a sample are dividing so that the number of cells present at anyone time t (measured in seconds) is growing exponentially according to the relationship y = 64 x 2^2t. it would be hard to check this relationship accurately by plotting measurements of y against t, so in practice one can use logarithms to convert it to a linear line equation. sketch a graph of log(base2)y against t, labelling the point where the graph crosses the axes?
how to i find the points on x and y-axis where the line crosses, i believe the line will be a straight line, how do i do this?

I REALLY HAVE TRIED WITH THIS QUESTION, IT HAS TAKEN ME THE WHOLE DAY TO TRY AND DO, I HOPE SOMEONE CAN SHOW ME HOW TO DO THIS :)
 
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  • #2
What, exactly, did you spend all day doing? Taking the logarithm of both sides of [itex]y= 64(2^{2t})[/itex] gives [itex]ln(y)= log(64)+ 2t log(2)[/itex]

That is of the form Y= at+ b where Y= log(y), a= 2log(2), and b= log(64). It crosses the Y axis when t= 0, at (0, ln(64)) and the t axis when Y= 0, at t= log(64)/(2log(2)).

I specifically did not give a base for the logarithm because the above is true for any base. It is particularly simple if you use, not "common" or "natural" logarithm, but the logarithm base 2: [itex]log_2(2)= 1[/itex] and [itex]log_2(64)= log_2(2^6)= 6[/itex] so Letting [itex]Y= log_2(y)[/itex], the equation becomes Y= 2t+ 6 with intercepts at (0, 6) and (3, 0).
 
  • #3
cheers mate, i wasnt doing that, i think i need to spend more time and concentration on logs and try a number of different questions on it, thanks again
 

Related to Exponential relationships to logarithms and straight line graph?

1. What is the relationship between exponential and logarithmic functions?

The relationship between exponential and logarithmic functions is that they are inverse operations of each other. In other words, the logarithm of a number is the exponent to which the base must be raised to equal that number. For example, log28 = 3, because 23 = 8.

2. How do you graph an exponential function?

To graph an exponential function, plot a few points by choosing values for the independent variable (usually x) and then calculating the corresponding values of the dependent variable (usually y). Then, connect the points with a smooth curve. The graph of an exponential function will either increase or decrease dramatically depending on the base of the function.

3. What is a logarithmic scale and when is it used?

A logarithmic scale is a scale in which values are spaced proportionally according to their logarithms. It is used when there is a large range of values to be plotted, as it compresses the scale and makes it easier to see the differences between values. It is commonly used in scientific and engineering fields.

4. How do you convert an exponential equation to a logarithmic equation?

To convert an exponential equation to a logarithmic equation, use the definition of logarithm: logbx = y if and only if by = x. The base of the logarithm will be the same as the base of the exponential function, and the exponent will be the same as the value of the independent variable.

5. Can an exponential function ever be a straight line?

Yes, an exponential function can be a straight line if the base of the exponential function is equal to 1. In this case, the graph of the function will be a horizontal line with a y-value of 1, since any number raised to the power of 0 is equal to 1.

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