When two chords intersect, each of them is divided into two line segments. Show that if the intersecting chords are of equal length, then the line segments of one chord are equal to the corresponding line segments of the other chord.
Let the two equal chords be and , intersecting at point . Let be the centre of the circle. We draw perpendiculars and from to and respectively. We are given that .
Since a perpendicular from the centre to a chord bisects it, is the midpoint of and is the midpoint of . Thus,
and
Because , we get and . Also, chords of equal length lie at equal distance from the centre, so .
Now, consider the right triangles and . We have , (common side), and . By the RHS congruence rule, . Hence, their corresponding parts are equal, giving .
Since and are midpoints, the segments of chord are:
and
(assuming is between and ). Similarly, for chord :
and
Substituting and , we get . Similarly, substituting and , we get .
∴ The line segments of one chord are equal to the corresponding line segments of the other chord.
Explanation
The proof leverages two key properties provided in the textbook context: first, that a perpendicular from the centre bisects a chord, and second, that equal chords are equidistant from the centre. By dropping perpendiculars from the centre to the two equal intersecting chords, we establish that the halves of the chords are equal, and the perpendicular distances are equal.
This sets up the conditions for the RHS congruency of the right triangles formed by the centre, the midpoint, and the point of intersection. Proving these triangles congruent shows that the distances from the intersection point to the midpoints are equal, which ultimately allows us to algebraically prove that the corresponding segments of the intersecting chords are equal.
Solution Steps
Step 1: Let equal chords and intersect at , with as the centre. Draw perpendiculars to and to .
Step 2: Apply the property that a perpendicular from the centre bisects the chord, so and . Since , and .
Step 3: Apply the property that equal chords are equidistant from the centre, so .
Step 4: In right triangles and , , , and . By RHS congruence, , meaning .
Step 5: Add/subtract the equal segments (, , etc.) to conclude and .