Math - solving equation

1. Sep 5, 2007

JPC

[SOLVED] Math - solving equation

1. The problem statement, all variables and given/known data

x belongs to Real numbers

2. Relevant equations

solving on paper
cos^2(x) - 4*cos(x) + (7 / 4 ) < 0

3. The attempt at a solution

no worthly attemps yet

2. Sep 5, 2007

sara_87

why don't you factorise it by using the completing the square thing or the ((-b)+or- (root(b^2) - 4ac) )/2a
...i think?

3. Sep 5, 2007

EnumaElish

To follow up on sara_87's post, let z = Cos(x). Now you have a quadratic equation (inequality) which you can solve for z.

Next time you have a similar question please post it under Pre-calculus Math.

4. Sep 5, 2007

HallsofIvy

Staff Emeritus
Why in the world is this in "other Sciences"?

5. Sep 7, 2007

JPC

well, i didnt see simply 'math' section , only saw 'calculus math' , didnt see 'Precalculus Mathematics' since i didnt have much time to post, sorry for wrong section. Next time ill know where to post for these types of questions

and btw, thx for your help, resolved it easily now

Last edited: Sep 7, 2007
6. Sep 7, 2007