Trig #3 (Part solutions included)

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Homework Help Overview

The discussion revolves around solving the inequality sec²x - 3secx + 2 < 0, which involves understanding the behavior of the secant function and its relationship to cosine. Participants are exploring the implications of the factored form of the inequality and the intervals where secx lies between 1 and 2.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the factorization of the inequality and its implications for the values of secx. There is a focus on determining the intervals for x based on the derived conditions. Some participants question whether they are correctly interpreting the inequality versus solving an equation.

Discussion Status

The conversation is ongoing, with some participants providing feedback on each other's interpretations and attempts. There is a recognition of the need to clarify the distinction between solving an inequality and an equation, and some guidance has been offered regarding the correct approach to finding solutions.

Contextual Notes

Participants are working within the constraints of the interval [0, 2π) and are considering the implications of the inequality on the values of x. There is an acknowledgment of the potential for multiple solutions across different intervals.

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Homework Statement



sec^2x - 3secx + 2 < 0


Homework Equations





The Attempt at a Solution



sec^2x - 3secx + 2 < 0

ok so this can be written as, (secx - 2)(secx -1) < 0
this means secx is between 1 and 2 right ?

secx = 2 and secx = 1

would we find all the solutions that's between 1 and 2 ?
please check if my understanding is correct.
 
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Sounds good.
 
lovemake1 said:

Homework Statement



sec^2x - 3secx + 2 < 0


Homework Equations





The Attempt at a Solution



sec^2x - 3secx + 2 < 0

ok so this can be written as, (secx - 2)(secx -1) < 0
this means secx is between 1 and 2 right ?

secx = 2 and secx = 1

would we find all the solutions that's between 1 and 2 ?
please check if my understanding is correct.
ab< 0 as long as a and b have different signs. Since 2> 1, secx- 2< secx- 1 so you want sec x- 2< 0 and sec x- 1> 0. That is, as you say, 1< sec x< 2.

secx= 1 is the same as 1/cosx= 1 or cos x= 1. sec x= 2 is the same as cos(x)= 1/2. and note that 1< 1/cos(x)< 2 is the same as cos(x)< 1< 2cos(x) or 1/2< cos(x)< 1.
Of course, if you are asked for all such x, not just between 0 and [itex]\pi/2[/itex] or 0 and [itex]2\pi[/itex], there will be many intervals in which that is true.
 
so the two solutions are, cosx = 1 and cosx = 1/2

since x belongs to [0,2pi), x = 0, 1/3pi
Could someone correct me if I am wrong, i think i got the right answer.
please check thanks
 
lovemake1 said:
so the two solutions are, cosx = 1 and cosx = 1/2

since x belongs to [0,2pi), x = 0, 1/3pi
Could someone correct me if I am wrong, i think i got the right answer.
please check thanks
No, this is not correct. You're forgetting that you're supposed to solve an inequality, not an equation. Reread HallsofIvy's post.
 
oh right, here are my fixed answer.

x belongs to (1pi/3, 1pi/3)

are they correct?
i didnt include 0, because x must be < cos = 1
 
Last edited:

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