how can I graph a log using a graphing calculator?

Question

jim_thompson5910 · Answer

type log(x)/log(b) into y1 to graph $$\large y=\log_{b}(x)$$

anonymous · Answer

thanks jim!

anonymous · Answer

if you have a log with a base (b) value of 10 then you just use the "log" button

anonymous · Answer

should it almost look like a radical graph?

anonymous · Answer

also, how could I find points using algebra?

anonymous · Answer

Put in a value for x and solve it for y. You can use that same formula from earlier (Change of Base Formula) to help put it in your calculator to get a decimal

jim_thompson5910 · Answer

Either plug in various values of x and evaluate, or bring up the table that will show you points that lie on the graph.

anonymous · Answer

but then I get x = 2^y...

anonymous · Answer

so if you have $$y=\log_{3}x$$ you can find a point by plugging in 9 for x and evaluating.
$$y=\log_{3}9$$
$$y=2$$
(9,2)

jim_thompson5910 · Answer

Solve for y to get $$\large y=\log_{2}(x)$$

Now plug in powers of 2

$$\large y=\log_{2}(1)=0$$

$$\large y=\log_{2}(2)=1$$

$$\large y=\log_{2}(4)=2$$

$$\large y=\log_{2}(8)=3$$

anonymous · Answer

so this is confusing. My log is $$y = \log_{2}{x}$$ so how come when i put in 1, and the square root of 1 is 1 I get something that doesn't match my graph. Using the trace feature it should be 0 when x = 1.

anonymous · Answer

Oo it looks like an exponent graph.. only.. different..

anonymous · Answer

If you put in 1 then you are saying $$2^?=1$$ ( I just re-wrote the problem as an exponential instead of a log) The only thing that will made an answer of 1 is the power 0.

Try using change of base instead so logx/log2 and put vlaues in for x now

jim_thompson5910 · Answer

it's the mirror of the exponential graph over the line y=x

You're not taking the square root of 1. You're asking yourself: the base (2) to what power (y) will give me 1? That answer is 0 since $$2^0=1$$

anonymous · Answer