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log base 4 , (x+1)exp3 divided by 2 =22

 Apr 12, 2016
 #1
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Solve for x:
(log^3(x+1))/(2 log^3(4)) = 22

(log^3(x+1))/(2 log^3(4)) = (log^3(x+1))/(2 log^3(4)):
(log^3(x+1))/(2 log^3(4)) = 22

Multiply both sides by 2 log^3(4):
log^3(x+1) = 44 log^3(4)

Taking cube roots gives 2^(2/3) 11^(1/3) log(4) times the third roots of unity:
log(x+1) = -((-11)^(1/3) 2^(2/3) log(4)) or log(x+1) = (-2)^(2/3) 11^(1/3) log(4) or log(x+1) = 2^(2/3) 11^(1/3) log(4)

log(x+1) = -(-11)^(1/3) 2^(2/3) log(4) has no solution since True (assuming the principal logarithm):
log(x+1) = (-2)^(2/3) 11^(1/3) log(4) or log(x+1) = 2^(2/3) 11^(1/3) log(4)

log(x+1) = (-2)^(2/3) 11^(1/3) log(4) has no solution since True (assuming the principal logarithm):
log(x+1) = 2^(2/3) 11^(1/3) log(4)

Cancel logarithms by taking exp of both sides:
x+1 = 4^(2^(2/3) 11^(1/3))

Subtract 1 from both sides:
Answer: |  x = 4^(2^(2/3) 11^(1/3))-1 =132.50

 Apr 12, 2016
 #2
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If the problem is:  log4 [ (x + 1)3 / 2 ]  =  22

Change from log form into exponential form:  (x + 1)3 / 2  =  422

Multiply both sides by 2:                                      (x + 1)3   =  2 · 422

Change the form of 422                                       (x + 1)3   =  2 · ( 2 · 2 )22

                                                                            (x + 1)3   =  2 · ( 22 )22

                                                                            (x + 1)3   =  2 · 244

Simplify:                                                               (x + 1)3   =  245 

Find the cube root of both sides:                             x + 1  =  215

Subtract 1 from both sides:                                           x  =  215 - 1  =  32768 - 1  =  32767

 

The cube root of 245 is  (245)1/3 =  245 x 1/3  =  215.

 Apr 12, 2016

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