SOLUTION: If limt(e^(ln(ax)) × tan(2a/x))= 8 ' find value of a ?

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Question 1204215: If limt(e^(ln(ax)) × tan(2a/x))= 8 ' find value of a ?
Found 2 solutions by MathLover1, ikleyn:
Answer by MathLover1(20850) About Me  (Show Source):
You can put this solution on YOUR website!

given:
lim%28x-%3E-infinity%2C%28e%5E%28ln%28ax%29%29%2Atan%28%282a%29%2Fx%29%29%29=+8
manipulate left side
lim%28x-%3E-infinity%2C%28e%5E%28ln%28ax%29%29%2Atan%28%282a%29%2Fx%29%29%29.........since e%5E%28ln%28ax%29%29=ax, we have

lim%28x-%3E-infinity%2C%28ax%2A+tan%28%282a%29%2Fx%29%29%29
then
lim%28x-%3E-infinity%2C+ax%2A+tan%28%282a%29%2Fx%29%29=++2a%5E2

equal it to right side

2a%5E2=8
a%5E2=4
a=2 =>solution
a=-2 =>not a solution
check:
lim%28x-%3E-infinity%2C%28e%5E%28ln%282x%29%29%2Atan%28%282%2A2%29%2Fx%29%29%29=+8
8=+8
lim%28x-%3Einfinity%2C%28e%5E%28ln%282x%29%29%2Atan%28%282%2A2%29%2Fx%29%29%29=+8
8=+8


Answer by ikleyn(52812) About Me  (Show Source):
You can put this solution on YOUR website!
.


        In the post by @MathLover1, this woman made very rude mistakes, which show that
        she not only does not know  Calculus,  but does not know the logarithmic function,  as well.

        Therefore, I will explain the solution from the very beginning.


If the problem asks about the limit  at x---> -oo,  then it is clear that the coefficient "a"
in this consideration must be negative - otherwise, logarithm  ln(ax)  is NOT DEFINED.


With negative "a", ln(ax) is defined at negative x, and  we can write  e%5Eln%28ax%29 = ax.


Then  

    lim%28x-%3E-infinity%2C+%28e%5E%28ln%28ax%29%29%2Atan%28%282a%29%2Fx%29%29%29 = lim%28x-%3E-infinity%2C+ax%2Atan%28%282a%29%2Fx%29%29 =  2a%5E2 = 8,


which implies a%5E2 = 4,  and since "a" is negative,  a = -2.


So, a = -2 is the only solution to this problem at x ---> -oo, which is exactly opposite to the conclusion by @MathLover1.


If the question is about finding "a" from this equation at x ---> oo,  then  the answer is  a = 2.


Thus, the ANSWER is twofold: if x ---> -oo,  then a = -2.

                             if x --->  oo,   then a = 2.

Solved.

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How this woman can call herself  " MathLover1 ",  making such errors,  is a mystery to me.