Trigonometric Equations...2

[nycmathguy]

Section 5.4

Question 70

Use: cos(x+A)=cosx.cosA–sinx.sinA

Let A = pi

cos(x + pi) = cosx(-1) - sinx(0)

cos(x + pi) = -cosx

-cosx - cosx - 1 = 0

-2cos x - 1 = 0

-2 cos x = 1

cos x = -1/2

Solutions from 0 to 2pi but not including 2pi:

x = 2pi/3, 4pi/3

You say?

 

[MathLover1]

correct

 

[nycmathguy]

correct

Wonderful. Before moving on to Section 5.5, there are several interesting questions at the end of Section 5.4 for which Ron Larson did not provide sample problems for me to use as a guide.