HELP PLZ C2 LOGS (i know theres one below, this is more specific)

heres the link to the original thread http://thestudentroom.co.uk/showthread.php?p=8710027#post8710027

Reply 1

.ACS.

I’ve seen question 10 come up quite a few times here before, in the past day or so. Just have a quick check and you should find it.

Reply 2

Notnek

I'm quite rusty with logs. Here's 11a:

a)
log, 4 (3) = (log,2 (3)) / (log,2 (4))
= 0.5log,2 (3)
= log,2 (root3)

OMG - being trying (b) for about 20 mins. Just realised they want you to
solve simutlaneous equations. I was trying to prove the second line given the first!

b)
2log,2 (y) = log,2 (root3) + log,2 (x)
y^2 = root3.x (1)

3^y = 9^x
3^y = (3^2)^x
= 3^2x

so y = 2x (2)

You can now solve the equations simultaneously.

Reply 3

PlaystationStudies

6: Start with the first equation. By logging both sides of the equation and then simplifying, you can find expressions for y in terms of x and vice versa. Then feed one of these values into the second equation. (Beware, answer involves fractions).

Reply 4

Notnek

This is good AEA practice!

Q12:
a)
3 + 2log,2 (x) = log,2 (y)
log,2 (8) + log,2 (x^2) = log,2 (y)
log,2 (8x^2) = log,2 (y)
8x^2 = y

b)
Using part (a) 14x - 3 is written intead of y

so 8x^2 = 14x - 3
(4x-1)(2x-3) = 0
a=0.25 b=1.5

c)
log,2 (a) = log,2 (0.25)
= log,2 (4)^-1
= -log,2 (4) = -2

d)
log,2 (b) = log,2 (3/2)

They asssume you can only do log base 10 on your calculator so:

log,2 (3/2) = lg(3/2) / lg(2)
= 0.585

Reply 5

maffsman

Hi you can find the answer to question 4 here: http://www.thestudentroom.co.uk/showthread.php?p=8710275#post8710275

Cos I'm stuck on the half the questions on that page too! From Q6 onwards

Reply 6

maffsman

Notnek, when you worked out 11b above I can understand what you've done but I cant do the simultaneous equations. I put in y=(2^x)²=x

\sqrt3

but what do I do next? I dont get any of this simultaneous equations when it involves logs.

Reply 7

Notnek

The two equations are:
(1) y^2 = x(root3)
(2) y = 2x

so x(root3) = 4x^2
x(4x - root3) = 0
x = 0, (root3 / 4)

Reply 8

gioms

numero 6)

8^y = 4^(2x+3)

2^3y = 2^(4x+6)

3y = 4x+6
y= 4x/3 = 2

log2 (y) = log2 (x) + 4
log2 (y/x) = 4

log2 ((4x/3 + 2)/x) = 4

2^4 = 4x+2/3x

48x = 4x =2

x= 1/22

y= 4/3 * 1/22 +2
= 68/33

seems to be an odd fraction.. is that the right answer?

Reply 9

uk_chip

wow i really wasnt expecting so much help thx everyone! but my exams r over edexcel C1 n C2 i know ill egt A's but im a bit pissed cos i cud have gotten 100% but i know i didnt :frown: