#i need help finding the domain of log(sin(x))

26 messages · Page 1 of 1 (latest)

naive zodiac
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the formula is {x ∈ dom(g) | g(x) ∈ dom(f)}

quaint pecanBOT
naive zodiac
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what i got so far is that

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f(x) = log(x) and g(x) = sin(x)

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and i put it into the formula but im not sure what to do

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since the dom(sin(x)) would be {x ∈ R} and dom(log(x)) would be {x ∈ R | x > 0}

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but if i put into the formula

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then i get {x ∈ R | sin(x) ∈ x > 0}

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but im not sure what to do next

compact spindle
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The domain is that sin(x) > 0

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as the input of a log function cannot be negative

naive zodiac
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ohh ok thanks

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do you know if you can help me out with finding the range?

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if you have the time

compact spindle
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Sure.

naive zodiac
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ill show you my working out

compact spindle
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So we know that sin(x) oscillates between -1 and 1, but in order to abide our restriction its going to be restricted to 0 < sin(x) <= 1. Note this is our input. Now the smaller the input the larger the negative exponent. Ex. log_10_(10^-1), log_10_(10^-10) as our input gets smaller and smaller i.e infinitely small towards 0, the larger the negative exponent gets. Now our largest input is 1. log_10_(1) = 0. Therefore I'd say the range is y <= 0

naive zodiac
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the formula to find the range(f(g(x)) is f(range(g) ∩ dom(f))

let f(x) = log(x) and let g(x) = sin(x)

so first i found the range(sin(x)) which was:
-1 ≤ x ≤ 1

then the domain of log(x) which was:
x > 0

then i substitute into the formula which got me:
log(x)(-1 ≤ x ≤ 1 ∩ x > 0)
and now i dont know what to do next

compact spindle
naive zodiac
naive zodiac
compact spindle
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The notation that you are using, I was not taught that notation.

naive zodiac
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ohh

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thank you anyways for the help

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really appreciate it 👍

naive zodiac
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