You are Here: Home >< A-levels

# c1 question: find the value of y such that 4^y+1=8^2y-1? watch

1. It's a question in one of the solomon papers. I have the answer but I don't understand how it comes to y=5/4?
2. (Original post by funkybinoculars)
It's a question in one of the solomon papers. I have the answer but I don't understand how it comes to y=5/4?
Change it, so they're in the same base.
3. (Original post by funkybinoculars)
It's a question in one of the solomon papers. I have the answer but I don't understand how it comes to y=5/4?
log everything

log(4)^y+1 + log(1) = log(8)^2y-1

use log rules

y+1log(4) + log(1) = 2y-1log(8)
log 1 is zero so:
y+1log(4) = 2y-1log(8)
divide both sides by log(4) and 2y-1

y+1/2y-1 = log(8)/log(4)
y+1/2y-1 = 3/2

multiply both sides by 2y-1 and 2
2y+2 = 6y-3
4y=5
y=5/4
4. (Original post by TheALevelStudent)
log everything

log(4)^y+1 + log(1) = log(8)^2y-1

use log rules

y+1log(4) + log(1) = 2y-1log(8)
log 1 is zero so:
y+1log(4) = 2y-1log(8)
divide both sides by log(4) and 2y-1

y+1/2y-1 = log(8)/log(4)
y+1/2y-1 = 3/2

multiply both sides by 2y-1 and 2
2y+2 = 6y-3
4y=5
y=5/4
yeah i thought about using log but don't know if i'd get a mark because we don't learn logs in c1?
5. (Original post by TheALevelStudent)
log everything

log(4)^y+1 + log(1) = log(8)^2y-1

use log rules

y+1log(4) + log(1) = 2y-1log(8)
log 1 is zero so:
y+1log(4) = 2y-1log(8)
divide both sides by log(4) and 2y-1

y+1/2y-1 = log(8)/log(4)
y+1/2y-1 = 3/2

multiply both sides by 2y-1 and 2
2y+2 = 6y-3
4y=5
y=5/4
No need. It is C1. Simple indices will resolve the issue here.

(Original post by funkybinoculars)
It's a question in one of the solomon papers. I have the answer but I don't understand how it comes to y=5/4?
Consider:

It shouldn't be difficult to see that x must be 3, because otherwise the sides won't be equal.

In the case of

Consider what base 4 and 8 have in common and convert both of them to that base, i.e if I had 9 I could write it as 3^2.

Once you have the same base, you know that you powers have to be the same (otherwise you won't have equality).

Can you go from here?
6. (Original post by funkybinoculars)
yeah i thought about using log but don't know if i'd get a mark because we don't learn logs in c1?
(Original post by kingaaran)
no need. It is c1. Simple indices will resolve the issue here.
log everything
7. (Original post by TheALevelStudent)
log everything
Better get memorising log tables for your C1 exam then
8. (Original post by kingaaran)
Better get memorising log tables for your C1 exam then
Lmao, I'm doing A2, so there is no need. In A2 we log everything 😂😂
9. (Original post by TheALevelStudent)
Lmao, I'm doing A2, so there is no need. In A2 we log everything 😂😂
Log (everything) = life
10. (Original post by kingaaran)
Log (everything) = life
You know it haha 😂😂

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: March 1, 2016
Today on TSR

### University open days

• Sheffield Hallam University
Wed, 17 Oct '18
• Northumbria University
Wed, 17 Oct '18
• Staffordshire University
Wed, 17 Oct '18
Poll

## All the essentials

### Student life: what to expect

What it's really like going to uni

### Essay expert

Learn to write like a pro with our ultimate essay guide.

### Create a study plan

Get your head around what you need to do and when with the study planner tool.

### Resources by subject

Everything from mind maps to class notes.

### Study tips from A* students

Students who got top grades in their A-levels share their secrets