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Sum of the Values of X, Exponential Equation 
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#1
Jul612, 05:39 AM

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1. The problem statement, all variables and given/known data
(4x)^(1 + log(base 2) (x)) = 8(x^3) What is the sum of the values of x that fullfill that equation? A) 2.5 B) 2.0 C) 1.5 D) 1.0 E) 0.5 2. Relevant equations Use the exponential equation only and make the lower one (exponented) 1. 3. The attempt at a solution (4x) = (2 x^(1/2))^2 8(x^3) = (2x)^3 If I insert x = (1/4) to make 4x = 1 it doesn't fulfill the equation.. So does x = (1/2).. I cannot simplify the exponential equation... Any assistance please? 


#2
Jul612, 06:20 AM

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hi wiraimperia!
(try using the X^{2} and X_{2} buttons just above the Reply box ) for any number n, what is n^{log2(x)} ? 


#3
Jul612, 07:00 AM

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[tex]4x(4x)^{\log_2x} = 8x^3[/tex]
... how many values of x satisfy the equation? I'd recheck for x=1/2 ... 


#4
Jul612, 10:18 AM

P: 9

Sum of the Values of X, Exponential Equation
I mean if it has 2 solutions, then we are asked X1 + X2, if it has 3, then X1 + X2 + X3, and so on...



#5
Jul612, 11:34 AM

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ehild 


#6
Jul612, 12:38 PM

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for any number m, what is (2^{m})^{log2(x)} ?



#7
Jul712, 01:42 AM

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Have you rechecked if x=1/2 is a solution? Personally I managed it by systematic guesswork using the list of possible solutions ... but I've had practice. Have you tried any of the other suggestions and hints? They are all good. Is there a particular method you are supposed to use or can we throw anything we like at the problem? eg. there's always bruteforce methods like plotting the curves to get ballpark figures and then using Newton/Raphson ... 


#8
Jul712, 01:50 AM

P: 3,807

Taking logarithm on both sides with base 2, you get:
[tex](1+log_2 x)log_2(4x)=3+3log_2 x[/tex] It is easy to solve now. 


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