8x^2 + 2x - 3 = 0
(4x )(2x )
(4x + 3)(2x - 1) = 0
Surprise: that might actually work.
4x + 3 =0
4x = - 3
x = - 3/4 That would be between 90 and 180 because the cos(x) is minus in quad 2.
2x - 1 = 0
2x = 1
x = 1/2 This one is actually only in quad 1.
cos(y) = 1/2
y = 60 degrees.
cos(y) = - 3/4
y = 138.6 degrees. You could do this by
cos(y) = 3/4
cos(y) = 41.4 degrees. Because the 3/4 is minus, the angle is in quad 2
180 - 41.4 = 138.6. Same answer.
The calculator does in the following way.
2nd F
Cos-1(
- 0.75
)
=
which will give you 138.6 immediately.