Find value of x on a chord in the circle - which of the statements is true

Question

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In the above image, is there a specific theorem that can be used to state which of the four statements must be true for x?

Answer 1

The chord labeled $a$ is shorter than the diameter which is $4\text{ cm}$. One segment of this chord is given as $1.5\text{ cm}$, so by difference the remains segment must be ... Uh-oh, gotta run. Can you finish?