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idk how you get y=10^3log+2 according to the mark scheme?
Original post by penelopecrux
idk how you get y=10^3log+2 according to the mark scheme?


Can you post your attempt?
Original post by penelopecrux
idk how you get y=10^3log+2 according to the mark scheme?


The straight line would be an equation in the form log(y)b=m[log(x)a]\log(y)-b=m[\log(x)-a] where mm is the gradient and (a,b)(a,b) a point that it passes through. Then just solve for yy.
Simply you have the equation of a straight line y = mx + c then you replace x,m and c with the equal terms from the graph. Leave y because the questions answer has y and not log10y as the function.
Original post by _gcx
Can you post your attempt?


this is my attempt
Original post by penelopecrux
this is my attempt


How can we "cancel" the logarithm on the LHS, to write the equation in the form y=f(x)y=f(x)?
Original post by _gcx
How can we "cancel" the logarithm on the LHS, to write the equation in the form y=f(x)y=f(x)?


would u write the 2 as log100?
Original post by penelopecrux
would u write the 2 as log100?


You could, but no point. Just think of an operation that gets rid off the log on the LHS, and apply it on both sides.
Original post by RDKGames
You could, but no point. Just think of an operation that gets rid off the log on the LHS, and apply it on both sides.


i'm not rlly sure tbh, all i can think to do is just to put the 3 up as a power to the x
Original post by penelopecrux
i'm not rlly sure tbh, all i can think to do is just to put the 3 up as a power to the x


What's the reverse operation of taking the logarithm??

If I wanted to find xx in 2x=82^x=8 and I would take the logarithm of both sides which gives log(2x)=log(8)\log(2^x)=\log(8)

So the reverse operation is to...?
(edited 7 years ago)
Original post by RDKGames
What's the reverse operation of taking the logarithm??

If I wanted to find xx in 2x=82^x=8 and I would take the logarithm of both sides which gives log(2x)=log(8)\log(2^x)=\log(8)

So the reverse operation is to...?


take logs of both sides?
Original post by penelopecrux
take logs of both sides?


No, you'd exponentiate both sides...

If I go back from log(2x)\log(2^x) I don't take logs to both sides, because then I'd have log(log(2x))\log(\log(2^x)).

Instead you need to take the expression and put it as the exponent to the base of the logarithm. So log(2x)=log(8)10log(2x)=10log(8)\log(2^x)=\log(8) \Rightarrow 10^{\log(2^x)}=10^{\log(8)} and it simplifies from there. (note that log\log is the same as log10\log_{10})

You may wish to review this in your chapter.
Original post by RDKGames
No, you'd exponentiate both sides...

If I go back from log(2x)\log(2^x) I don't take logs to both sides, because then I'd have log(log(2x))\log(\log(2^x)).

Instead you need to take the expression and put it as the exponent to the base of the logarithm. So log(2x)=log(8)10log(2x)=10log(8)\log(2^x)=\log(8) \Rightarrow 10^{\log(2^x)}=10^{\log(8)} and it simplifies from there. (note that log\log is the same as log10\log_{10})

You may wish to review this in your chapter.


yeah but how do i do that with the equation i have currently?
logy=logx^3 +2)
Original post by penelopecrux
yeah but how do i do that with the equation i have currently?
logy=logx^3 +2)


If we exponentiate xx (with base 10), then we have 10x10^x. How can we therefore exponentiate both sides of this equation?
Original post by _gcx
If we exponentiate xx (with base 10), then we have 10x10^x. How can we therefore exponentiate both sides of this equation?


i rly dont know
Original post by penelopecrux
i rly dont know


10log10(y)=y=103log10(x)+210^{\log_{10}(y)}=y=10^{3\log_{10}(x)+2} and simplify RHS.

Again, you may wish to review this chapter - this is a very basic principle.
Original post by RDKGames
10log10(y)=y=103log10(x)+210^{\log_{10}(y)}=y=10^{3\log_{10}(x)+2} and simplify RHS.

Again, you may wish to review this chapter - this is a very basic principle.


yeah i'll definitely give it a review

i just don't get how logy turns into that??
apologies for all this :tongue:
Original post by penelopecrux
yeah i'll definitely give it a review

i just don't get how logy turns into that??
apologies for all this :tongue:


ab=cloga(ab)=loga(c)bloga(a)=1=loga(c)\displaystyle a^b=c \Rightarrow \log_a(a^b)=\log_a(c) \Rightarrow b \underbrace{\log_a(a)}_{=1}=\log_a(c)

so b=loga(c)b=\log_a(c)

Happy with this??

Now start with the RHS

b=loga(c)ab=aloga(c)ab=c=aloga(c)b=\log_a(c) \Rightarrow a^b=a^{\log_a(c)} \Rightarrow a^b=c=a^{\log_a(c)} which in other words means aloga(c)=ca^{\log_a(c)}=c
(edited 7 years ago)

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