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How do you find the angles that satisfy sin(x) = -0.5?

To determine the angles that satisfy the equation sin(x)=0.5\sin(x) = -0.5, we can utilize the properties of the unit circle and the sine function.

First, it’s important to remember that the sine function is periodic, with a period of 360360^\circ (or 2π2\pi radians). This periodicity implies that the sine of an angle will repeat every 360360^\circ. Additionally, the sine function exhibits symmetry about 180180^\circ (or π\pi radians), which aids in identifying all possible solutions.

On the unit circle, the sine of an angle equals 0.5-0.5 at specific locations. The primary angle where sin(x)=0.5\sin(x) = -0.5 is at 210210^\circ (or 7π6\frac{7\pi}{6} radians) in the third quadrant. Another angle where sin(x)=0.5\sin(x) = -0.5 occurs at 330330^\circ (or 11π6\frac{11\pi}{6} radians) in the fourth quadrant. These two angles represent the principal solutions within one complete cycle of 360360^\circ.

To find all possible solutions, we can leverage the periodic nature of the sine function. For any integer kk, the general solutions can be expressed as:

x=210+360korx=330+360k(in degrees)x = 210^\circ + 360^\circ k \quad \text{or} \quad x = 330^\circ + 360^\circ k \quad \text{(in degrees)}

or, equivalently,

x=7π6+2πkorx=11π6+2πk(in radians).x = \frac{7\pi}{6} + 2\pi k \quad \text{or} \quad x = \frac{11\pi}{6} + 2\pi k \quad \text{(in radians)}.

In these equations, kk represents any integer, which accounts for the infinite number of cycles the sine function can undergo. By adding multiples of 360360^\circ (or 2π2\pi radians), we can identify all angles that satisfy the equation sin(x)=0.5\sin(x) = -0.5.

Answered by: Dr. Sarah Wilson
GCSE Physics Tutor
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