C1 and C2 Maths, AQA, 24/05/10

What did people get for the very last question on core 1?

What did people get for the very last question on core 1?

8eii was a bit odd, I noticed you could get it into the form of a previous part to show k = 10

Using that, I ended up with 2^(4x) = 10, so 4xlog2 = 1, and x = 1/(4log2)

The part in a previous question to deduce that the curve had no max points was weird. I had a reason why, but I don't think it was the right method.

Edit: Method as far as I can remember.

Previous part:
$log_a k = 3log_a 2 + log_a 5 - log_a 4$

$k = 10$


Part eii:
$2^{4x-3} = \frac{5}{4}$

$log_{10} 2^{4x} - 3log_{10} 2 = log_{10} \frac{5}{4}$

$log_{10} 2^{4x} = log_{10} {10}$

$2^{4x} = 10$

$4xlog_{10} 2 = 1$

$x = \frac{1}{4log_{10} 2}$

This was the only question I didn't manage.. I think I'm missing something.
How did you get from the first to the second line of working out? As in what rules and things?
Thanks

3log2 becomes log 8
using the fact that loga + logb = logab, log8 + log 5 = log40
then using the fact that loga - logb = log(a/b), log40 - log4 = log10
Given that logk = log10, k = 10

Ok, thankyou, I did manage that bit. But then for 8eii), how did you do that??

What did people get for the very last question on core 1?

-1/7 <= k <= 1

me too... I think I got full marks except for the last question of #1..

uh yeah hadn't seen a question like that before... think i got the answer in the end though

well I originally worked the co ords to be (-6,0) and whilst reading through my answers with one minute left to go I realised this couldn't be right, -6 had to be +ve... so I subbed x = 6 in and got (6,12/5) as didn't have time to do the working prior..

I proabably won't even get one mark if it's right, what do you think?