Intermediate Geometry : Plane Geometry

Study concepts, example questions & explanations for Intermediate Geometry

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Example Questions

Example Question #41 : Trapezoids

Find the value of \(\displaystyle c\) if the area of the trapezoid below is \(\displaystyle 60\).

3

Possible Answers:

\(\displaystyle 10\)

\(\displaystyle 12\)

\(\displaystyle 6\)

\(\displaystyle 8\)

Correct answer:

\(\displaystyle 8\)

Explanation:

The formula to find the area of a trapezoid is

\(\displaystyle \text{Area}=\frac{1}{2}(base_1+base_2)(height)\).

Substitute in the values for the area, a base, and the height. Then solve for \(\displaystyle c\).

\(\displaystyle 60=\frac{1}{2}(12+c)6\)

\(\displaystyle 120=(12+c)6\)

\(\displaystyle 12+c=20\)

\(\displaystyle c=8\)

 

Example Question #42 : Trapezoids

Find the value of \(\displaystyle d\) if the area of the trapezoid below is \(\displaystyle 210\).

12

Possible Answers:

\(\displaystyle 14\)

\(\displaystyle 8\)

\(\displaystyle 12\)

\(\displaystyle 10\)

Correct answer:

\(\displaystyle 12\)

Explanation:

The formula to find the area of a trapezoid is

\(\displaystyle \text{Area}=\frac{1}{2}(base_1+base_2)(height)\).

Substitute in the values for the area, a base, and the height. Then solve for \(\displaystyle d\).

\(\displaystyle 210=\frac{1}{2}(18+d)14\)

\(\displaystyle 420=(18+d)14\)

\(\displaystyle 18+d=30\)

\(\displaystyle d=12\)

 

Example Question #43 : Trapezoids

The area of the trapezoid below is \(\displaystyle 96\). Find the length of \(\displaystyle AD\).

4

Possible Answers:

\(\displaystyle 12\)

\(\displaystyle 20\)

\(\displaystyle 16\)

Cannot be determined from the information given.

Correct answer:

\(\displaystyle 20\)

Explanation:

Start by drawing in the height, \(\displaystyle CE\), to form a right triangle.

4a

Use the Pythagorean Theorem to find the length of \(\displaystyle CE\).

\(\displaystyle 8^2+(CE)^2=10^2\)

\(\displaystyle 64+(CE)^2=100\)

\(\displaystyle (CE)^2=36\)

\(\displaystyle CE=6\)

Now that we have the height, plug in the given information into the formula to find the area of the trapezoid.

Keep in mind that \(\displaystyle AE+ED=AD\).

\(\displaystyle \text{Area}=\frac{1}{2}(base_1+base_2)(height)\)

\(\displaystyle 96=\frac{1}{2}(12+AE+8)(6)\)

\(\displaystyle \frac{1}{2}(AE+20)=16\)

\(\displaystyle AE+20=32\)

\(\displaystyle AE=12\)

The question asks you to find the length of \(\displaystyle AD\).

\(\displaystyle AD=AE+ED\)

\(\displaystyle AD=12+8=20\)

 

 

Example Question #44 : Trapezoids

Find the length of \(\displaystyle AD\). The area of the trapezoid is \(\displaystyle 56\). Round to the nearest hundredths place.

6

Possible Answers:

\(\displaystyle 11.56\)

\(\displaystyle 12.15\)

\(\displaystyle 9.42\)

Cannot be determined from the information given.

Correct answer:

\(\displaystyle 12.15\)

Explanation:

First, draw in the height \(\displaystyle CE\).

6a

First, find \(\displaystyle CE\) by using \(\displaystyle \text{sine}\).

\(\displaystyle \sin 47=\frac{CE}{8}\)

\(\displaystyle CE=8 \sin 47=5.85\)

Now, plug in the values for area, height, and one base to find the length of the second base, \(\displaystyle AD\).

\(\displaystyle \text{Area}=\frac{1}{2}(base_1+base_2)(height)\)

\(\displaystyle 56=\frac{1}{2}(7+AD)(5.85)\)

\(\displaystyle \frac{1}{2}(7+AD)=9.57\)

\(\displaystyle 7+AD=19.15\)

\(\displaystyle AD=12.15\)

Example Question #45 : Trapezoids

The area of the trapezoid below is \(\displaystyle 244\). Find the length of \(\displaystyle AD\). Round to the nearest hundredths place.

10

Possible Answers:

\(\displaystyle 57.12\)

\(\displaystyle 94.12\)

\(\displaystyle 56.23\)

\(\displaystyle 67.41\)

Correct answer:

\(\displaystyle 57.12\)

Explanation:

First, draw in the height.

10a

First, find the height by using \(\displaystyle \text{sine}\).

\(\displaystyle \sin 62=\frac{height}{8}\)

\(\displaystyle height=8\sin 62=7.06\)

Now, plug in the values for area, height, and one base to find the length of the second base, \(\displaystyle AD\).

\(\displaystyle \text{Area}=\frac{1}{2}(base_1+base_2)(height)\)

\(\displaystyle 244=\frac{1}{2}(12+AD)(7.06)\)

\(\displaystyle \frac{1}{2}(12+AD)=34.56\)

\(\displaystyle 12+AD=69.12\)

\(\displaystyle AD=57.12\)

Example Question #46 : Trapezoids

The area of the trapezoid below is \(\displaystyle 124\). Find the length of \(\displaystyle AD\). Round to the nearest hundredths place.

11

Possible Answers:

\(\displaystyle 16.34\)

\(\displaystyle 15.25\)

\(\displaystyle 11.14\)

\(\displaystyle 19.54\)

Correct answer:

\(\displaystyle 15.25\)

Explanation:

First, draw in the height.

11a

First, find the height by using \(\displaystyle \text{sine}\).

\(\displaystyle \sin 58=\frac{height}{10}\)

\(\displaystyle height=10\sin 58=8.48\)

Now, plug in the values for area, height, and one base to find the length of the second base, \(\displaystyle AD\).

\(\displaystyle \text{Area}=\frac{1}{2}(base_1+base_2)(height)\)

\(\displaystyle 124=\frac{1}{2}(14+AD)(8.48)\)

\(\displaystyle \frac{1}{2}(14+AD)=14.62\)

\(\displaystyle 14+AD=29.25\)

\(\displaystyle AD=15.25\)

Example Question #47 : Trapezoids

Given: Quadrilateral \(\displaystyle ABCD\) such that \(\displaystyle \overline{AB} \parallel \overline{CD}\) and \(\displaystyle \overline{AD} \ncong \overline{BC}\)

True, false, or undetermined: Quadrilateral \(\displaystyle ABCD\) is a trapezoid.

Possible Answers:

Undetermined

True

False

Correct answer:

True

Explanation:

Quadrilateral \(\displaystyle ABCD\) has at least one pair of parallel sides, \(\displaystyle \overline{AB}\) and \(\displaystyle \overline{CD}\). The figure is, by definition, a parallelogram if and only if \(\displaystyle \overline{AD} \parallel \overline{BC}\), and, by definition, a trapezoid if and only if \(\displaystyle \overline{AD} \nparallel \overline{BC}\). Opposite sides of a parallelogram are also congruent; since \(\displaystyle \overline{AD} \ncong \overline{BC}\), Quadrilateral \(\displaystyle ABCD\) is not a parallelogram. It is therefore a trapezoid.

Example Question #48 : Trapezoids

A trapezoid has height 20 inches and area 640 square inches. Which of these choices can represent the lenghts of the two bases of the trapezoid?

Possible Answers:

2 inches and 60 inches

18 inches and 44 inches

32 inches and 32 inches

25 inches and 35 inches

27 inches and 37 inches

Correct answer:

27 inches and 37 inches

Explanation:

We can apply the area formula here.

\(\displaystyle A = \frac{1}{2} h \left ( B+b\right )\)

\(\displaystyle 640 = \frac{1}{2}\cdot 20 \left ( B+b\right )\)

\(\displaystyle 640 = 10 \left ( B+b\right )\)

\(\displaystyle B + b = 64\)

The sum of the bases must be 64 inches. We check each one of these choices, except for 32 inches and 32 inches, which can be eliminated as the bases cannot be of the same length.

\(\displaystyle 27+37=64\)

\(\displaystyle 25+35=60\)

\(\displaystyle 18+44=62\)

\(\displaystyle 2+60=62\)

Only 27 and 37 have 64 as a sum, so this is the correct choice.

Example Question #1 : How To Find If Kites Are Similar

A kite has two different side lengths of \(\displaystyle 4\) and \(\displaystyle 12\). Find the measurements for a similar kite. 

Possible Answers:

\(\displaystyle 3\) and \(\displaystyle 8\)

\(\displaystyle 6\) and \(\displaystyle 36\)

\(\displaystyle 5\) and \(\displaystyle 18\)

\(\displaystyle 8\) and \(\displaystyle 24\)

\(\displaystyle 2\) and \(\displaystyle 4\)

Correct answer:

\(\displaystyle 8\) and \(\displaystyle 24\)

Explanation:

A kite is a geometric shape that has two sets of equivalent adjacent sides. In order for two kites to be similar their sides must have the same ratios. 

Since, the given kite has side lengths \(\displaystyle 4\) and \(\displaystyle 12\), they have the ratio of \(\displaystyle 4:12=1:3\).

Therefore, find the side lengths that have a ratio of \(\displaystyle 1:3\).

The only answer choice with this ratio is: \(\displaystyle 8:24=1:3\)

Example Question #2 : How To Find If Kites Are Similar

A kite has two different side lengths of \(\displaystyle 6\) and \(\displaystyle 24\). Find the measurements for a similar kite. 

Possible Answers:

\(\displaystyle 5\) and \(\displaystyle 20\)

\(\displaystyle 1\) and \(\displaystyle 6\)

\(\displaystyle 6\) and \(\displaystyle 3\)

\(\displaystyle 2\) and \(\displaystyle 5\)

\(\displaystyle 7\) and \(\displaystyle 30\)

Correct answer:

\(\displaystyle 5\) and \(\displaystyle 20\)

Explanation:

A kite is a geometric shape that has two sets of equivalent adjacent sides. In order for two kites to be similar their sides must have the same ratios. 

The given side lengths for the kite are \(\displaystyle 6\) and \(\displaystyle 24\), which have the ratio of \(\displaystyle 1:4\)

The only answer choice with the same relationship between side lengths is: \(\displaystyle 5\) and \(\displaystyle 20\), which has the ratio of \(\displaystyle 1:4.\)

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