# C3 Differentiation question urgent help!Watch

Announcements
#1
Show that y=xsin(x) has a stationary point when x=-tan(x)

how do i go about this? I know i use the product rule but do I substitute -tanx into y=xsinx and then differentiate or what? then what do i do?

thanks!
0
5 years ago
#2
(Original post by Mr Tall)
Show that y=xsin(x) has a stationary point when x=-tan(x)

how do i go about this? I know i use the product rule but do I substitute -tanx into y=xsinx and then differentiate or what? then what do i do?

thanks!
product rule states that if y = uv then dy/dx = uv' + vu'

so let u = x and v = sinx

the order doesn't actually matter.
0
#3
(Original post by Mike_123)
product rule states that if y = uv then dy/dx = uv' + vu'

so let u = x and v = sinx

the order doesn't actually matter.
but how do i show it has a stationary point when x=-tanx
0
5 years ago
#4
(Original post by Mr Tall)
Show that y=xsin(x) has a stationary point when x=-tan(x)

how do i go about this? I know i use the product rule but do I substitute -tanx into y=xsinx and then differentiate or what? then what do i do?

thanks!
If the question said "find the stationary point of y=xSinx" what would you do
0
5 years ago
#5
(Original post by Mr Tall)
but how do i show it has a stationary point when x=-tanx
A stationary point means the first derivative is 0.
0
#6
(Original post by TenOfThem)
If the question said "find the stationary point of y=xSinx" what would you do
yeap im aware that at a stationary point dy/dx=0

would i sub -tanx into y=xsinx and then show that it equals zero or what?

thanks
0
5 years ago
#7
(Original post by Mr Tall)
yeap im aware that at a stationary point dy/dx=0

would i sub -tanx into y=xsinx and then show that it equals zero or what?

thanks
0
5 years ago
#8
A stationary point of a function is a point at which the gradient of the curve of that function is 0. Therefore, you need to differentiate the function using the product rule, and then equate the answer to 0. Shuffle the terms around to get the equation that was given to you.
0
5 years ago
#9
(Original post by WK_Of_Angmar)
...
DO you understand why the forum rules ask us not to give full solutions?
0
5 years ago
#10
(Original post by TenOfThem)
DO you understand why the forum rules ask us not to give full solutions?
0
5 years ago
#11
(Original post by WK_Of_Angmar)
Fair enough
0
5 years ago
#12
(Original post by Mr Tall)
Show that y=xsin(x) has a stationary point when x=-tan(x)

how do i go about this? I know i use the product rule but do I substitute -tanx into y=xsinx and then differentiate or what? then what do i do?

thanks!
Yes you do and make it equal to zero, assuming you have a value for X
0
5 years ago
#13
You could sub -tanx in, I don't think it would get you anywhere.
Start off differentiating y=xsinx as you usually would, and equate it to zero.
This will involve utilising trig identities.
0
5 years ago
#14
(Original post by Mr Tall)
yeap im aware that at a stationary point dy/dx=0

would i sub -tanx into y=xsinx and then show that it equals zero or what?

thanks
You're not substituting anything. You're working towards that answer. It should become obvious if you've done it correctly.
0
5 years ago
#15
(Original post by charlesturner8)
Yes you do and make it equal to zero, assuming you have a value for X
No
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 (301)
30.9%
The paper was reasonable (394)
40.45%
Not feeling great about that exam... (158)
16.22%
It was TERRIBLE (121)
12.42%