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# C2 Logarithms

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1. Is it a valid thing to do to put log in front of every term of an equation or will this change what the equation means?.
2. Yer this is fine you can go from x^2 + 5 = 8 to 2logx +log5 =log8

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3. (Original post by C.L-A)
Yer this is fine you can go from x^2 + 5 = 8 to 2logx +log5 =log8

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Ok awesome thank you for the help.
4. Please forget what the person before said. Remember one rule of logarithms: ln(xy)= lnx+lny?
ln(x+y) is not necessarily lnx+lny. You can put a log in front of every equation, in the way that
x^2+5=8 is like ln(x^2+5)=ln8. But just claiming that a sum inside a log is like a sum outside a log is incorrect... and fairly stupid as well.
5. (Original post by C.L-A)
Yer this is fine you can go from x^2 + 5 = 8 to 2logx +log5 =log8

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No, you can't do that!
take the equation again:

x^2 + 5 = 8, yeah?

Now simplify: x^2 = 3.

If you log both sides now, 2logx = log3.

However by what you did, 2logx + log5 = log 8.

log3 is not equal to log8-log5.

What you did is wrong. You can't do that.
6. (Original post by RizK)
No, you can't do that!
take the equation again:

x^2 + 5 = 8, yeah?

Now simplify: x^2 = 3.

If you log both sides now, 2logx = log3.

However by what you did, 2logx + log5 = log 8.

log3 is not equal to log8-log5.

What you did is wrong. You can't do that.
So why is this wrong and in what circumstances is it the correct thing to do? do you have to simplify all of the terms first?
7. (Original post by Mackiemcmasher)
So why is this wrong and in what circumstances is it the correct thing to do? do you have to simplify all of the terms first?
If you do something to one side of the equal sign you must do the same to the other therefore put the whole thing inside a bracket then log the whole thing. Or simplify, whatever you wish

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Updated: May 22, 2016
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