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What is the value of \(x\) to the nearest tenth?

[tex]\[
\cos (50 + x)^{\circ} = \sin (2x - 6)^{\circ}
\][/tex]

A. 0
B. 46
C. 15.3
D. 44
E. 18.7

Sagot :

To solve the equation \(\cos (50 + x)^\circ = \sin (2x - 6)^\circ\), we can use trigonometric identities to simplify and solve for \( x \).

1. Use the identity: \(\sin \theta = \cos (90^\circ - \theta)\)

Therefore, \(\sin (2x - 6)^\circ = \cos \left(90^\circ - (2x - 6)^\circ\right) = \cos (96^\circ - 2x)^\circ\).

2. Rewrite the equation:
[tex]\[ \cos (50 + x)^\circ = \cos (96 - 2x)^\circ \][/tex]

3. Equate the angles:
For two cosines to be equal, the angles must be congruent to each other modulo \(360^\circ\), so we have:
[tex]\[ 50 + x = 96 - 2x + 360k \quad \text{or} \quad 50 + x = -96 + 2x + 360k \][/tex]
for \(k \in \mathbb{Z}\).

4. Solve the first equation:
[tex]\[ 50 + x = 96 - 2x + 360k \][/tex]
[tex]\[ 3x = 46 + 360k \][/tex]
[tex]\[ x = \frac{46 + 360k}{3} \][/tex]

For \(k = 0\):
[tex]\[ x = \frac{46}{3} \approx 15.3 \][/tex]

For \(k = 1\):
[tex]\[ x = \frac{406}{3} \approx 135.3 \][/tex]

For \(k = -1\):
[tex]\[ x = \frac{-314}{3} \approx -104.7 \][/tex]

5. Solve the second equation:
[tex]\[ 50 + x = -96 + 2x + 360k \][/tex]
[tex]\[ 50 + x = -96 + 2x + 360k \][/tex]
[tex]\[ 50 + 96 = x + 360k \][/tex]
[tex]\[ x = 146 + 360k \][/tex]

For \(k = 0\):
[tex]\[ x = 146 \][/tex]

6. Check the values for each \(k\), and realistic solutions:
We are only interested in the values \(0 \leq x < 360\).

Therefore, the candidates \( x \approx 15.3, 135.3, -104.7, 146 \). Within \(0 \leq x < 360\), appropriate values are \( 15.3 \) and \(146\).

7. Compare with given choices \(0, 46, 15.3, 44, 18.7^\circ \):
The nearest tenth from our solution set is \(15.3 \).

Therefore, the value of [tex]\( x \)[/tex] to the nearest tenth is [tex]\(15.3^\circ\)[/tex].