Question

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Answer 1

@pseudparse do you know Pythagoras?

Answer 2

Just see this figure, AB be a tangent
A line drawn from center ( radius) makes 90 degrees with the tangent. In your question there are three line segments which seem like tangent but only one is a tangent.
Check which one of the triangle satisfies Pythagoras

Answer 3

In triangle ABG
\[AB=6\]
\[AG= (4+4)\]
\[BG=4\]
\[6^2+4^2 \ne 8^2\]
so AB is not a tangent!!
Check the other two?

Answer 4

Yeah, good:D

Answer 5

Did you understand?