Question

solve cos theta x cos 2 theta=1/✓2​

Answer 1

Answer

If cosθ=c, then

2c

2

−1=

2

2

+1

❤️❤️

(

2

c−1)

or (

2

c−1)[(

2

c+1)−(1+

2

1

)]=0

or (

2

c−1)

2

(c−

2

1

)=0

∴c=

2

1

,

2

1

∴θ=2nπ±

4

π

or 2nπ±

3

π

.