ISEE Upper Level Math : Chords

Study concepts, example questions & explanations for ISEE Upper Level Math

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Example Questions

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Example Question #21 : Circles

Chords

Figure NOT drawn to scale

In the above diagram, evaluate .

Possible Answers:

Correct answer:

Explanation:

If two chords of a circle intersect inside the circle, the product of the lengths of the parts of each chord is the same. In other words,

Solving for :

Simplifying the radical using the Product of Radicals Principle, and noting that 25 is the greatest perfect square factor of 50:

Example Question #22 : Circles

Secant

In the above figure,  is a tangent to the circle.

Evaluate .

Possible Answers:

Correct answer:

Explanation:

If a secant segment and a tangent segment are constructed to a circle from a point outside it, the square of the distance to the circle along the tangent is equal to the product of the distances to the two points on the circle along the secant; in other words,

,

and, substituting, 

Distributing and writing in standard quadratic polynomial form,

We can factor the polynomial by looking for two integers with product  and sum 24; through some trial and error, we find that these numbers are 32 and , so we can write this as 

By the Zero Product Principle, 

, in which case  - impossible since  is a (positive) distance; or,

, in which case  - the correct choice.

Example Question #23 : Circles

Chords

Figure NOT drawn to scale

In the above diagram, evaluate .

Possible Answers:

Correct answer:

Explanation:

If two chords of a circle intersect inside the circle, the product of the lengths of the parts of each chord is the same. In other words,

Solving for :

Simplifying the radical using the Product of Radicals Principle, and noting that the greatest perfect square factor of 96 is 16:

Example Question #24 : Circles

Secant

Figure NOT drawn to scale

In the above figure,  is a tangent to the circle.

Evaluate .

Possible Answers:

Correct answer:

Explanation:

If a secant segment line and a tangent segment are constructed to a circle from a point outside it, the square of the length of the tangent is equal to the product of the distances to the two points on the circle intersected by the secant; in other words,

Substituting:

Distributing, then solving for :

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