How many real values for are there that satisfy the below equation?
Details:
This problem is a part of <Christmas Streak 2017> series .
This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try
refreshing the page, (b) enabling javascript if it is disabled on your browser and,
finally, (c)
loading the
non-javascript version of this page
. We're sorry about the hassle.
Relevant wiki: Properties of Logarithms - Basic
Using the basic rules of logarithms, we can simplify the equation to lo g x − 1 { 6 1 ( − x + 4 ) ( − x 3 + 7 x 2 − 1 3 x + 9 ) } = 0 .
Since the antilogarithm must equal 1, we can write ( x − 4 ) ( x 3 − 7 x 2 + 1 3 x − 9 ) = 6 .
Simplifying this, we get ( x − 1 ) ( x − 2 ) ( x − 3 ) ( x − 5 ) = 0 .
Then are there 4 values for x ?
Woah, wait, no, hold on there for a sec. Calm down.
We're taking the real logarithm. Check if the base is positive and not equal to 1, and also if the antilogarithm isn't negative.
If x = 1 , the base is equal to 0 . Then all the logs aren't defined.
If x = 2 , the base is equal to 1 . Similarly, all the logs aren't defined.
If x = 3 , the equation would look like: lo g 2 6 1 + lo g 2 1 + lo g 2 6 = 0 . Makes perfect sense.
If x = 5 , the second and third antilogarithm is negative. Then those two logs aren't defined.
From above, we can figure out that there is only 1 value for x , which is 3 .
(P.S. If you type this up in wolframalpha, it'll tell you x = 1 or 3. Defeating the computer is easy. >w>)