Both the red and blue line segments stretch from the center of the circle to a
point on the circle. the length of the blue line segment is 7. how long is the
red line segment?

It is also 7.

Explanation:

Any line from the center of the circle to a point on the circle is the radius. Any line drawn from the center of a circle to a point on the circle is equal to any other line drawn likewise, irrespective of if this line is going up, down, left, right, etc.

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