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C1 paper question help?

Can anyone help me with part b) of this question? thanks!

The answer is x=1/3
(edited 9 years ago)
Original post by Tommehh
Can anyone help me with part b) of this question? thanks!


Can you do it after noting

4x+1=4×4x4^{x+1}=4 \times 4^x

2x×4×4x=4×8x2^{x} \times 4 \times 4^x = 4 \times 8^{x}
(edited 9 years ago)
Reply 2
Original post by SamKeene
Can you do it after noting

4x+1=4×4x4^{x+1}=4 \times 4^x

2x×4×4x=4×8x2^{x} \times 4 \times 4^x = 4 \times 8^{x}


No:confused: can you please run through the rest of the method? thanks for your time.
2^x times 4^(x+1) is the same as 2^x times 2^2(x+1) since 4=2^2. Basically breaking it down so you have 2 to the power of something throughout
2^x times 2^(2x+2) therefore equals 2^(3x+2) which equals 8 or 2^3. since you have 2 to the power of something on both sides, both powers must be the same total, so 3x+2 equals 3. Basic equations follow to find x.
Original post by Tommehh
No:confused: can you please run through the rest of the method? thanks for your time.


2x×4×4x=4×8x2^{x} \times 4 \times 4^x = 4 \times 8^{x}

4×8x=84 \times 8^x = 8

8x=28^x = 2

x=log82x=\log_8 2

I'm sure you can finish it from there.
Reply 5
Original post by SamKeene
2x×4×4x=4×8x2^{x} \times 4 \times 4^x = 4 \times 8^{x}

4×8x=84 \times 8^x = 8

8x=28^x = 2

x=log82x=\log_8 2

I'm sure you can finish it from there.


I dont understand how you arrived at your second line of working looking at your first? Need to revise this topic:s-smilie:
Original post by Tommehh
I dont understand how you arrived at your second line of working looking at your first? Need to revise this topic:s-smilie:


2x×4x+1=82^{x} \times 4^{x+1} = 8

2x×4×4x=82^{x} \times 4 \times 4^x = 8

4×8x=84 \times 8^{x} = 8

Should clear it up.
Just put everything to a power of 2. for example, 4 to the power of x+1 becomes 2 to the power of 2x+2 and 8 becomes 2 to the power 3. Then x+2x+2 equals 3, so X=one third. See above for a more number-y version.
If you still need help, Without using logarithms because that's C2 you do;
Not sure how to do maths thing but try to read it,
(2^x) X (4^x+1) = 8
(2^x) X ((2^2)^x+1) = 2^3
so simplify then add the powers: (2^x) X (2^2x+2) = 2^3 => (2^3x+2) = 2^3 => 3x+2=3 => 3x=1 => x=1/3
Original post by AngelaMckenzie
If you still need help, Without using logarithms because that's C2 you do;
Not sure how to do maths thing but try to read it,
(2^x) X (4^x+1) = 8
(2^x) X ((2^2)^x+1) = 2^3
so simplify then add the powers: (2^x) X (2^2x+2) = 2^3 => (2^3x+2) = 2^3 => 3x+2=3 => 3x=1 => x=1/3


Didn't notice this was C1... this is most likely the intended method. Use this OP.
Original post by keromedic
I don't think that's valid working.


Where is it invalid?

Edit: Unless you missed the context where I was considering the LHS only for the first line?
Original post by keromedic
I don't think that's valid working.

There's no rule that states that an×bn=(a×b)na^n \times b^n=(a \times b)^n


It's valid, it's just that it's using logarithms and that's in C2 :tongue:

2^2 x 4^2 = 64
8^2 = 64
Original post by SamKeene
Where is it invalid?

Edit: Unless you missed the context where I was considering the LHS only for the first line?


Ignore me

Original post by AngelaMckenzie
....


Please don't post full solutions. Haven't gone through the working but OP, she has the right idea. Getting everything in terms of 2. The (a) part was supposed to suggest that, I think.
(edited 9 years ago)
Original post by AngelaMckenzie
It's valid, it's just that it's using logarithms and that's in C2 :tongue:

2^2 x 4^2 = 64
8^2 = 64


Ignore me, I'm a fool.
Reply 14
Original post by AngelaMckenzie
If you still need help, Without using logarithms because that's C2 you do;
Not sure how to do maths thing but try to read it,
(2^x) X (4^x+1) = 8
(2^x) X ((2^2)^x+1) = 2^3
so simplify then add the powers: (2^x) X (2^2x+2) = 2^3 => (2^3x+2) = 2^3 => 3x+2=3 => 3x=1 => x=1/3


Thanks so much:biggrin: have a nice easter!

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