# Solve Trigonometry equations with cos (x + α) - cos (x - α) = c and sin (x + α) - sin (x - α) = c

To
solve a form equation

Cos (x + α) ± cos (x – α) = c dan sin (x + α) ± sin (x –
α) = c

You
can use the sine and cosine multiplication formula that we have learned in
school, namely:

2 sin α cos β = sin (α + β) + sin (α - β)

2 cos α sin β = sin (α + β) - sin (α - β)

2 cos α cos β = cos (α + β) + cos (α + β)

- 2 sin α sin β = cos (α + β) - cos (α - β)

**Example 1.**

Determine the set of completion equations
Sin
(x + 210)

^{0}+ sin (x – 210)^{0}=1/2√3 , for 0 ≤ x ≤ 360.
Answers:

X = - 30 + k . 360 or x = (180 – (- 30)) + k . 360 = 210 + k . 360,
k
is an integer. For intervals 0 ≤ x ≤ 360, then by choosing the appropriate k
obtained x = 210 or x = 330.

So,
the settlement set is {210, 330}.

**Example 2.**

Determine
the set of resolutions from the equation Sin
(x + 135)

^{0}– sin (x – 135)^{0}= 1, for 0 ≤ x ≤ 360.
Answers:

x = 45 +
k. 360 or x = -45 + k. 360, k are integers. So the solution is {45, 315}

**Example 3**

Determine
the set of resolutions from the equation,

X = 5/4 π + k . 2 π or x = (π – 5/4 π) + k . 2 π = ½ π + k . 2 π, k are
integers. For intervals of 0 ≤ x ≤ 360, then selecting k accordingly is
obtained x = 5/4 π or 7/4 π. So,
the solution is {5/4 π, 7/4 π}.

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