SAT II Math II : 2-Dimensional Geometry

Study concepts, example questions & explanations for SAT II Math II

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Example Questions

Example Question #8 : Finding Sides

Regular Pentagon  has perimeter 35.  has  as its midpoint; segment  is drawn. To the nearest tenth, give the length of .

Possible Answers:

Correct answer:

Explanation:

The perimeter of the regular pentagon is 35, so each side measures one fifth of this, or 7. Also, since  is the midpoint of 

Also, each interior angle of a regular pentagon measures .

Below is the pentagon in question, with  indicated and  constructed; all relevant measures are marked. 

Pentagon 1

A triangle  is formed with , and included angle measure . The length of the remaining side can be calculated using the law of cosines: 

where  and  are the lengths of two sides,  is the measure of their included angle, and  is the length of the third side. 

Setting , and , substitute and evaluate :

;

Taking the square root of both sides:

,

the correct choice.

Example Question #9 : Finding Sides

Regular Hexagon  has perimeter 360.  and  have  and as midpoints, respectively; segment  is drawn. To the nearest tenth, give the length of .

Possible Answers:

Correct answer:

Explanation:

The perimeter of the regular hexagon is 360, so each side measures one sixth of this, or 60. Since  is the midpoint of 

Similarly, .

Also, each interior angle of a regular hexagon measures .

Below is the hexagon with the midpoints  and , and with  constructed. Note that perpendiculars have been drawn to  from  and , with feet at points and  respectively.

Hexagon

 is a rectangle, so .

This makes  and  the short leg and hypotenuse of a 30-60-90 triangle; as a consequence,

.

For the same reason,

Adding the segment lengths:

.

Example Question #10 : Finding Sides

Regular Pentagon  has perimeter 60. 

To the nearest tenth, give the length of diagonal .

Possible Answers:

Correct answer:

Explanation:

The perimeter of the regular pentagon is 60, so each side measures one fifth of this, or 12. Also, each interior angle of a regular pentagon measures .

The pentagon, along with diagonal , is shown below:

Pentagon 2

 

A triangle  is formed with , and included angle measure . The length of the remaining side can be calculated using the Law of Cosines: 

where  and  are the lengths of two sides,  the measure of their included angle, and  the length of the side opposite that angle.

Setting , and , substitute and evaluate :

Taking the square root of both sides:

,

the correct choice.

Example Question #51 : Geometry

Given a cube, if the volume is 100 feet cubed, what must be the side?

Possible Answers:

Correct answer:

Explanation:

Write the formula for the volume of the cube.

To solve for , cube root both sides.

Substitute the volume.

The answer is:  

Example Question #1 : Angles

Solve for and .

Question_3

(Figure not drawn to scale).

Possible Answers:

Correct answer:

Explanation:

The angles containing the variable  all reside along one line, therefore, their sum must be .

Because  and  are opposite angles, they must be equal.

Example Question #2 : Finding Angles

What angle do the minute and hour hands of a clock form at 6:15?

Possible Answers:

Correct answer:

Explanation:

There are twelve numbers on a clock; from one to the next, a hand rotates . At 6:15, the minute hand is exactly on the "3" - that is, on the  position. The hour hand is one-fourth of the way from the "6" to the "7" - that is, on the  position. Therefore, the difference is the angle they make:

.

Example Question #3 : Finding Angles

In triangle  and . Which of the following describes the triangle?

Possible Answers:

 is acute and isosceles.

 is obtuse and scalene.

 is acute and scalene.

 is obtuse and isosceles.

None of the other responses is correct.

Correct answer:

 is acute and isosceles.

Explanation:

Since the measures of the three interior angles of a triangle must total 

All three angles have measure less than , making the triangle acute. Also, by the Isosceles Triangle Theorem, since ; the triangle has two congruent sides and is isosceles. 

Example Question #1 : Finding Angles

In  and  are complementary, and . Which of the following is true of  ?

Possible Answers:

 is right and isosceles.

 is acute and scalene.

 is right and scalene.

None of the other responses is correct.

 is acute and isosceles.

Correct answer:

 is right and scalene.

Explanation:

 and  are complementary, so, by definition, 

Since the measures of the three interior angles of a triangle must total 

 is a right angle, so  is a right triangle. 

 and  must be acute, so neither is congruent to ; also,  and   are not congruent to each other. Therefore, all three angles have different measure. Consequently, all three sides have different measure, and  is scalene.

Example Question #1 : Finding Angles

Decagon

The above figure is a regular decagon. Evaluate .

Possible Answers:

Correct answer:

Explanation:

As an interior angle of a regular decagon,  measures

.

Since  and  are two sides of a regular polygon, they are congruent. Therefore, by the Isosceles Triangle Theorem,

The sum of the measures of a triangle is , so

Example Question #2 : Finding Angles

Hexagon

The above hexagon is regular. What is ?

Possible Answers:

None of the other responses is correct.

Correct answer:

Explanation:

Two of the angles of the quadrilateral formed are angles of a regular hexagon, so each measures

.

The four angles of the quadrilateral are . Their sum is , so we can set up, and solve for  in, the equation:

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