# e^x+e^-x=2.5Watch

Announcements
#1
e^x+e^-x=2.5

So the way I have solved this is

e^x+1/e^-x-2.5=0
e^2x+1-2.5e^x=0

equating to y=e^x
y^2-2.5y+1=0
2y^2-5y+2=0
(2y-1)(y-2)
e^x=1/2 e^x=2

therefore x= ln0.5 or ln2

The textbook says the answer is +/-ln2.

Where did I go wrong?

Thanks
0
5 years ago
#2
(Original post by elia)
Where did I go wrong?

You didn't

1
5 years ago
#3
You've got it correct. The answers are the same.
1
#4
(Original post by J10)
You've got it correct. The answers are the same.
Ah yes checked in the calculator, I always assume I'm wrong :/

Thanks guys!
0
5 years ago
#5
(Original post by elia)
Ah yes checked in the calculator, I always assume I'm wrong :/

Thanks guys!
You should not need to check on the calculator

ln(1/2) = - ln(2)

Rules of logs
0
5 years ago
#6
(Original post by TenOfThem)
You should not nee to check on the calculator

ln(1/2) = - ln(2)

Rules of logs
I'd have solved the equation (she can write the answer straight down from the formula book).
0
X

new posts
Latest
My Feed

### Oops, nobody has postedin the last few hours.

Why not re-start the conversation?

see more

### See more of what you like onThe Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

### University open days

• Arts University Bournemouth
Art and Design Foundation Diploma Further education
Sat, 25 May '19
• SOAS University of London
Wed, 29 May '19
• University of Exeter
Thu, 30 May '19

### Poll

Join the discussion

#### How did your AQA GCSE Physics Paper 1 go?

Loved the paper - Feeling positive (491)
31.1%
The paper was reasonable (608)
38.51%
Not feeling great about that exam... (258)
16.34%
It was TERRIBLE (222)
14.06%