Subject: trig functions

Name: melissa
Who is asking: Student
Level: Secondary

Question:
Find all solutions in the interval (0,2pi)
2cos²x-3cosx-4=0

I think i should graph it but can't figure out how to enter cos²x into my calculator. Also, can this be used with the quadratic formula? i have no clue what I'm doing.

For either the graphic solution or the algebraic solution it is important to realize that cos²x = (cos x)(cos x) = (cos x)².

To enter cos²x into your calculator, calculate cos x and square it. For an algebraic solution write y = cos x and then the equation becomes 2 y² - 3 y - 4 = 0.