Finding the Gradient of Stationary Points in Trigonometric Functions

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Homework Help Overview

The discussion revolves around finding the gradient of stationary points for the function y = 1 - 2sin(x) within the domain 0 < x < 2π. Participants are exploring the implications of differentiating the function and determining where it crosses the x-axis.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss differentiating the function and setting the derivative to zero to find stationary points. There is confusion about whether to find the gradient at stationary points or the gradient itself. Some participants suggest solving for when the function equals zero to find x-axis intersections.

Discussion Status

The conversation is active, with participants questioning each other's interpretations and clarifying the problem statement. Some guidance has been offered regarding the differentiation process and the conditions for finding x-axis crossings, but no consensus has been reached on the final values or methods.

Contextual Notes

There is a noted change in the problem statement regarding the domain of the function, which has led to further exploration of the implications for finding gradients at specific points. Participants are also working with the constraints of not having calculators available for exact calculations.

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Homework Statement


gradient of the stationary points of y=1-2sinx domain 0<x<2pi

Homework Equations


The Attempt at a Solution


dy/dx = -2cosx
-2cosx=0...?
 
Last edited:
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Gradient of the stationary point? Do you need to find that or the gradient? Because when you put dy/dx=0 it sort of implies what the gradient will be.
 
rock.freak667 said:
Gradient of the stationary point? Do you need to find that or the gradient? Because when you put dy/dx=0 it sort of implies what the gradient will be.

Sorry. the qu reads 'the curve y=1-2sinx has domain 0<x<pi. find the gradients of the curve at the points where the curve crosses the x-axis
 
pip_beard said:
Sorry. the qu reads 'the curve y=1-2sinx has domain 0<x<pi. find the gradients of the curve at the points where the curve crosses the x-axis

Ah that is different.

Well you know the gradient function is dy/dx.

You need to find when the curve crosses the x-axis, or when y=0.
 
so do i differentiate it and make it = 0?

so i get -2cosx=0
 
pip_beard said:
so do i differentiate it and make it = 0?

so i get -2cosx=0

how to i rearrange this to work it out?
 
pip_beard said:
so do i differentiate it and make it = 0?

so i get -2cosx=0

pip_beard said:
how to i rearrange this to work it out?

No if y=1-2sinx, the curve crosses, the x-axis when y=0

so solve 1-2sinx=0 for x. Can you do that?
 
-2sinx=1
sinx=-1/2
 
pip_beard said:
-2sinx=1
sinx=-1/2

which gives x as ? ( in the given domain that is)
 
  • #10
principle value of -0.523 (but out of range) the pi-(-0.523) = 3.6651

therfore value = 3.6651 and 6.2832?
 
  • #11
pip_beard said:
-2sinx=1
sinx=-1/2

pip_beard said:
principle value of -0.523 (but out of range) the pi-(-0.523) = 3.6651

therfore value = 3.6651 and 6.2832?



this should be sinx=1/2.


But how did you get that value for x?
 
  • #12
ohhh... did sin^-1... so ...

x principle = 0.479425
so pi - 0.4879425 = 2.66216
 
  • #13
pip_beard said:
ohhh... did sin^-1... so ...

x principle = 0.479425
so pi - 0.4879425 = 2.66216

you should get x= π/6 and another one, best to use the exact values, I don't have a calculator with me to divide out pi.
 
  • #14
ok. i'll have a play and post back if i can't do it.. Thanks for the inspiration!
 

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