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# C2 Logarithms question Watch

1. This is a worked example that I have a question on.

Find, to three significant figures, the value of log8 11

Take logs to base 10 of each side.
log10 (8x)=log10 11

x log10 8=log10 11

x= log10 11/ log10 8

x=1.15

I do not understand the point where they just time both sides by log10. Why do they do this. Also HOW is the statement that log10 (8x)=log10 11 actually true?

Thanks so much
2. (Original post by krisshP)
This is a worked example that I have a question on.

Find, to three significant figures, the value of log8 11

Take logs to base 10 of each side.
log10 (8x)=log10 11

x log10 8=log10 11

x= log10 11/ log10 8

x=1.15

I do not understand the point where they just time both sides by log10. Why do they do this. Also HOW is the statement that log10 (8x)=log10 11 actually true?

Thanks so much

log10 is not a number it is a function so they have not multiplied by it, they have taken logs of both sides

Applying a function to both sides of an equation is something that you have been doing, probably since Y7
3. (Original post by krisshP)
This is a worked example that I have a question on.

Find, to three significant figures, the value of log8 11

Take logs to base 10 of each side.
log10 (8x)=log10 11

x log10 8=log10 11

x= log10 11/ log10 8

x=1.15

I do not understand the point where they just time both sides by log10. Why do they do this. Also HOW is the statement that log10 (8x)=log10 11 actually true?

Thanks so much
They aren't multiplying both sides by log to base 10, they are taking logs to base 10 of both sides as the example says.
In other words, if a=b, then f(a)=f(b).
4. (Original post by TenOfThem)
log10 is not a number it is a function so they have not multiplied by it, they have taken logs of both sides

Applying a function to both sides of an equation is something that you have been doing, probably since Y7
Okay, thanks

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