SAT Math : How to find the angle of a sector

Study concepts, example questions & explanations for SAT Math

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Example Questions

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

Inscribed quad

Figure NOT drawn to scale.

The above figure shows a quadrilateral inscribed in a circle. Evaluate .

Possible Answers:

The question cannot be answered from the information given. 

Correct answer:

Explanation:

If a quadrilateral is inscribed in a circle, then each pair of its opposite angles are supplementary - that is, their degree measures total .

 and  are two such angles, so 

Setting  and , and solving for :

,

the correct response.

Example Question #281 : Plane Geometry

Inscribed quad

Figure NOT drawn to scale.

The above figure shows a quadrilateral inscribed in a circle. Evaluate .

Possible Answers:

The question cannot be answered from the information given. 

Correct answer:

The question cannot be answered from the information given. 

Explanation:

If a quadrilateral is inscribed in a circle, then each pair of its opposite angles are supplementary - that is, their degree measures total .

 and  are two such angles, so 

Setting  and , and solving for :

,

The statement turns out to be true regardless of the value of . Therefore, without further information, the value of  cannot be determined.

Example Question #281 : Sat Mathematics

Inscribed quad

Figure NOT drawn to scale.

The above figure shows a quadrilateral inscribed in a circle. Evaluate .

Possible Answers:

Correct answer:

Explanation:

If a quadrilateral is inscribed in a circle, then each pair of its opposite angles are supplementary - that is, their degree measures total .

 and  are two such angles, so 

Setting  and , and solving for :

,

the correct response.

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

Secant 2

Figure NOT drawn to scale.

Refer to the above diagram.  is a diameter. Evaluate 

Possible Answers:

Correct answer:

Explanation:

  is a diameter, so  is a semicircle - therefore, . By the Arc Addition Principle,

If we let , then

,

and

If a secant and a tangent are drawn from a point to a circle, the measure of the angle they form is half the difference of the measures of the intercepted arcs. Since  and  are such segments intercepting  and , it holds that

Setting , and :

The inscribed angle that intercepts this arc, , has half this measure:

.

This is the correct response.

Example Question #12 : How To Find The Angle Of A Sector

Secant 3Figure NOT drawn to scale.

In the above figure,  is a diameter. Also, the ratio of the length of  to that of  is 7 to 5. Give the measure of 

Possible Answers:

The measure of  cannot be determine from the information given.

Correct answer:

Explanation:

 is a diameter, so  is a semicircle, which has measure . By the Arc Addition Principle,

If we let , then, substituting:

,

and

the ratio of the length of  to that of  is 7 to 5; this is also the ratio of their degree measures; that is,

Setting  and :

Cross-multiply, then solve for :

, and 

If a secant and a tangent are drawn from a point to a circle, the measure of the angle they form is half the difference of the measures of the intercepted arcs. Since  and  are such segments whose angle  intercepts  and , it holds that:

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