Subject: trig functions

Name: melissa

Who is asking: Student

Level: Secondary

Question:

Find all solutions in the interval (0,2pi)

2cos^{2}x-3cosx-4=0

I think i should graph it but can't figure out how to enter cos^{2}x into my calculator.
Also, can this be used with the quadratic formula? i have no clue what I'm doing.

Hi Melissa,
For either the graphic solution or the algebraic solution it is important to realize that cos^{2}x = (cos x)(cos x) = (cos x)^{2}.

To enter cos^{2}x into your calculator, calculate cos x and square it. For an algebraic solution write y = cos x and then the equation becomes 2 y^{2} - 3 y - 4 = 0.

Cheers,

Paul and Harley