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Home Q & A Board Science-Related Homework Help Mathematics
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Lexyz Lexyz
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12 years ago
How would I solve the equation 2^2x+2^x-56=0 to get x=ln7/ln2. I have no clue how they got that answer can somebody please explain it to me?
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tommyqtommyq
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#1
12 years ago
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#2
12 years ago
let 2^x=t then the equation becomes

t^2+t-56=0
for which the solution is
[t+8] [t-7]=0
 t=-8,7

so 2^x=-8, 7

2^x=7
taking the log we get
xln2=ln7
x=ln7\ln2

we ignore [-8] value as log of negitive is not possible.
wrote...
#3
12 years ago
put 2^x=a the equation bcums
a^2+a-56=0
a=-8,7
2^x=7(since 2^x cant be negative)
Taking ln on both sides
xln2=ln7
x=ln7/ln2
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