Cos(x) = -0.7, 2Ï€ x < 4Ï€?

Question

solve this on the specified interval

i tried but i dont know.

thanks so much

Answer 1

If you mean the interval between 2pi and 4pi, this is pretty easy to do.  cos(x) behaves in this interval just like it does between 0 and 2pi.  It is negative in the 2 and 3d quadrants.

Since cos(pi/4)=0.707, the 2 values will be close to 2pi+3pi/4 and 2pi+5pi/4