Question

Find the general solution and find the specific solutions over the interval [0,4pi]

Answer 1

Answer:

Isolate the angle 2x, by following the reverse "order of operations".

Step-by-step explanation:

Explanation:

Step 1: Add 1 to both sides:

2

cos

2

(

2

x

)

=

1

Step 2: Divide both sides by 2:

cos

2

(

2

x

)

=

1

2

Step 3: Take the square root of both sides:

cos

(

2

x

)

=

√

2

2

or

cos

(

2

x

)

=

−

√

2

2

(don't forget the positive and negative solutions!)

Step 4: Use inverse of cosine to find the angles:

2

x

=

cos

−

1

(

√

2

2

)

or

2

x

=

cos

−

1

(

−

√

2

2

)

Step 5: Find angles that work:

2

x

=

π

4

or

2

x

=

7

π

4

or

2

x

=

3

π

4

or

2

x

=

5

π

4

Step 6: Solve for x:

x

=

π

8

,

7

π

8

,

3

π

8

,

5

π

8

or .785, 5.5, 2.36, 3.93

(decimal approximations are seen on the graph below)