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 #1
avatar+4473 
+5

For g(x)=4^x, notice that we can say y = g(x) = 4^x or y is a function of x. The same goes for y = f(x) = log(5)x. 

For g(x)=4^x: To find the x-intercept, we need to set y = 0 --> y = g(x) = 0 = 4^x or simply, 0 = 4^x. Now, if we plug in any values not includng 0 for x such as x = -5, -4, -3, -1, 1, 2, etc. we get y-values that are NOT 0. Therefore, the x-intercept does not exist. If we graph g(x)=4^x, we notice that as the x-values reach negative infinity, the y-values are closer and closer to the 0 value but never 0. Therefore, there is no x-intercept.

To find the y-intercept, we need to set x = 0 --> y= g(x) = 4^0 = 1. Any number to a power of 0 is equal to 1. Now, notice that if we tried plugging in x = 0 first when we were finding the x-intercept, we would have already found the y-intercept without noticing! Therefore, the y-intercept = 1 at the point (0,1).

f(x)=log(5)x: To find the x-intercept, we need to set y = 0 --> y = f(x) = 0 = log(5)x. Since this is a log function, it is best to observe the behavior of the graph since plugging in points may be a bit too tedious. It is best to use the properties of logs to find the intercept(s). 0 = log(5)x. The log, in this case, is in the log based 10 form (log 10). So by properties of logs, we can do the following: 10^0 = 10^(log10(5)x) --> 1 = 5x [10 to the power of log based 10 cancels out leaving the 5x] --> Now, the algebra is simple and we divide both sides by 5 to obtain x = 1/5 = 0.2. However, by looking at the graph, we notice that the graph is symmteric. Therefore, the x-intercepts would be at 0.2 and -0.2 at the points (0.2, 0) & (-0.2, 0).

To find the y-intercept, we need to set x = 0 --> y = f(x) = log(5)0 = log(0). Notice that we have y = log 0 and there is no x anywhere which means there is no y-intercept since x = 0 becomes log 0 which is a continous function when graphed, the y-value goes to negative infinity because of the nature of the log 0 graph. There is no y-intercept.

Jul 25, 2014
 #2
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Jul 25, 2014
 #233
avatar+118723 
+3

@@ End of Day Wrap :  Fri 25/7/14      Sydney, Australia     Time 12:35 am   (Really Saturday morning)   ♬

Hi all,             

Great answers were provided today by Alan, DevikaAnand Heureka, CPhill, AzizHusain, Stu, Zegroes, Rosala, Kitty3, NinjaDevo and DragonSlayer554.  Thank you all.  

 

Ninja has completed his first draft of 'Great Answers to Learn From' and he is looking for comments and input from other members.  

You may want to suggest that another thread be included.

You may want to suggest that a thread be moved from where Ninja has put it to somewhere else. Remember, Ninja has not done a lot of these topics so it is possible that some things are not in the best places.

You may have something else on your mind that I have not thought of.

I am very pleased with the thread that Ninja has put together.  It is very nicely presented and over the course of time I feel sure that it will be well used.

Ninja, On behalf of web2.0 forum I offer you a very big thank you.  Rosala might have some roses for you if you are really lucky.  

http://web2.0calc.com/questions/great-answers-to-learn-from-rough-draft

----------------------------------------------------

This is an interesting little question. Thanks Alan

http://web2.0calc.com/questions/1-sqrt-3-2-sqrt-3-1-why

 It is already Saturday for me.  You are all headed to your weekend.  Make sure that you enjoy it.

That is it for tonight.   Adios.

                                                          ♬ ♬ MELODY ♬ ♬

Jul 25, 2014
 #1
avatar+3454 
+5
Jul 25, 2014
 #1
avatar+118723 
+3

x²-2x-4≥0

first solve   $$x^2-2x-4=0$$

NO factors are jusmping out at me so you couold solve it usingthe quadratic formula

a=1,  b=-2 and c = -4

http://www.youtube.com/watch?v=O8ezDEk3qCg 

I'm going to try and get this answer using the the site calc

$${\frac{\left({\mathtt{2}}{\mathtt{\,\small\textbf+\,}}{\sqrt{{\mathtt{4}}{\mathtt{\,\small\textbf+\,}}{\mathtt{16}}}}\right)}{{\mathtt{2}}}} = {\mathtt{3.236\: \!067\: \!977\: \!499\: \!789\: \!7}}$$

$${\frac{\left({\mathtt{2}}{\mathtt{\,-\,}}{\sqrt{{\mathtt{4}}{\mathtt{\,\small\textbf+\,}}{\mathtt{16}}}}\right)}{{\mathtt{2}}}} = -{\mathtt{1.236\: \!067\: \!977\: \!499\: \!789\: \!7}}$$

so the roots are approx  x=3.2 and x=-1.2

$$y=x^2-2x-4$$     is a concave up (Because the number in fornto of the x^2 is positive) parabola (x^2)

If you scketch it on a peice of paper you will see that y is above 0 at the 2 endss so

$$x\le -1.2\qquad and\qquad x \ge 3.2$$    correct to one dec place.    

 I think that is all ok,  If you need more explanation then aske for it.  

Jul 25, 2014
 #3
avatar+11912 
0
Jul 25, 2014

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