+0  
 
+1
231
3
avatar

7^a -7^a-5=117642√7

 

Find the value of a

Guest Nov 6, 2017
 #1
avatar+544 
-1

There is no solution for a.

 

 

laughlaughlaugh

ProMagma  Nov 6, 2017
 #2
avatar+89775 
+1

I  think this might be

 

7^a -7^(a-5)=117642√7

 

We  can write

 

7^a -  7^a / 7^5  = (2 * 3 * 2801) * 7 * 7^(1/2)

 

7^a -  7^a / 7^5  = (2 * 3 * 2801) *  7^(3/2)    multiply through  by  7^5

 

7^(a + 5)  - 7^a  = (2 * 3 * 2801) *  7^(13/2)      factor

 

7^a ( 7^5 - 1)  =   (2 * 3 * 2801) *  7^(13/2)    

 

7^a ( 16806) =  ( 16806) * 7^(13/2)         divide  out  16806

 

7^a  =  7^(13/2)

 

a ⇒  13/2

 

 

cool cool cool

CPhill  Nov 6, 2017
 #3
avatar
0

Solve for a:
7^a - 7^(a - 5) = 117642 sqrt(7)

 

Simplify and substitute x = -7^(a - 5).
7^a - 7^(a - 5) = -16806 (-7^(a - 5))
 = -16806 x:
-16806 x = 117642 sqrt(7)

 

Divide both sides by -16806:
x = -7 sqrt(7)

 

Substitute back for x = -7^(a - 5):
-7^(a - 5) = -7 sqrt(7)

 

Multiply both sides by -1:
7^(a - 5) = 7 sqrt(7)

 

Take the logarithm base 7 of both sides:
a - 5 = (log(7 sqrt(7)))/(log(7))

 

Add 5 to both sides:
a = 5 + (log(7 sqrt(7)))/(log(7))

Log here is the natural "ln".

Guest Nov 6, 2017
edited by Guest  Nov 7, 2017

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