What is the exact value of x?

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Answer 1 · 2017-12-19T15:56:18

#x = log(3.2)/(5 log 21)#

Given:

#5 * 21^(5x) = 16#

Divide both sides by #5# to get:

#21^(5x) = 16/5 = 3.2#

Transpose and take the log of both sides to get:

#log 3.2 = log (21^(5x)) = 5x log 21#

Divide both ends by #5 log 21# and transpose to find:

#x = log(3.2)/(5 log 21)#

So the fourth option is the correct one.