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When an object travels slower than sound, the ratio in this equation is greater than one, and the equation does not have a real solution. Traveling at the speed of sound makes the ratio equal one and results in a Mach angle of ninety degrees. Above the speed of sound, the ratio is less than one and the Mach angle is less than ninety degrees. The faster the object moves, the narrower the cone of high pressure behind it becomes. Measuring the vertex angle is a way to determine the speed of a supersonic object.
Reference 4: Screenshots from the Video below.
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