Here's the key:
Any radius that's perpendicular to a chord, bisects the chord.
So the piece of a radius that's perpendicular to the chord bisects it,
and the part of the chord that forms a side of the triangle is also 6.5 .
The triangle is a right triangle, and its hypotenuse is a radius of the circle.
the diameter of the circle is 16, so the length of the radius is 8 .
So now you know the length of the hypotenuse and one leg of a right
triangle, and side 'x' is the other leg.
This is where Pythagoras comes in.
(hypotenuse)² = (one leg)² + (the other leg)²
(8)² = (6.5)² + x²
64 = 42.25 + x²
x² = 64 - 42.25
x² = √21.75
x = about 4.664... (looks like choice-A)
