ISEE Upper Level Quantitative : Sectors

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

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Example Questions

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Example Question #191 : Plane Geometry

Tangents 1

Figure NOT drawn to scale.

Refer to the above diagram.  is the arithmetic mean of  and .

Which is the greater quantity?

(a) 

(b) 

 

Possible Answers:

(b) is the greater quantity

(a) and (b) are equal

It is impossible to determine which is greater from the information given

(a) is the greater quantity

Correct answer:

(a) and (b) are equal

Explanation:

 is the arithmetic mean of  and , so

By arc addition, this becomes

Also, , or, equivalently,

, so

Solving for :

Also,

 

If two tangents are drawn to a circle, the measure of the angle they form is half the difference of the measures of the arcs they intercept, so

 

Example Question #17 : How To Find The Angle Of A Sector

Inscribed angle 4

Figure NOT drawn to scale

In the above diagram, .

Which is the greater quantity?

(a) 

(b) 

Possible Answers:

(a) and (b) are equal

(b) is the greater quantity

(a) is the greater quantity

It is impossible to determine which is greater from the information given

Correct answer:

(a) and (b) are equal

Explanation:

 is a right triangle whose hypotenuse  has length  times that of leg . This is characteristic of a triangle whose acute angles both have measure  -and consequently, whose acute angles are congruent. Therefore,

These inscribed angles being congruent, the arcs they intercept,  and , are also congruent.

 

Example Question #11 : How To Find The Angle Of A Sector

Inscribed angle 4

Figure NOT drawn to scale

In the above diagram, .

Which is the greater quantity?

(a) 

(b) 

Possible Answers:

(b) is the greater quantity

It is impossible to determine which is greater from the information given

(a) is the greater quantity

(a) and (b) are equal

Correct answer:

(a) is the greater quantity

Explanation:

 is an inscribed angle, so its degree measure is half that of the arc it intercepts, :

.

 and  are acute angles of right triangle . They are therefore complimentary - that is, their degree measures total . Consequently,

.

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