Intermediate Geometry : Acute / Obtuse Isosceles Triangles

Study concepts, example questions & explanations for Intermediate Geometry

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Example Questions

Example Question #1 : How To Find The Area Of An Acute / Obtuse Isosceles Triangle

An isosceles triangle is placed in a circle as shown by the figure below.

1

If the diameter of the circle is , find the area of the shaded region.

Possible Answers:

Correct answer:

Explanation:

2

From the given image, you should notice that the base of the triangle is also the diameter of the circle. In addition, the height of the triangle is also the radius of the circle.

Thus, we can find the area of the triangle.

Next, recall how to find the area of a circle.

To find the area of the shaded region, subtract the two areas.

Make sure to round to  places after the decimal.

Example Question #21 : Triangles

An isosceles triangle is placed in a circle as shown by the figure below.

1

If the diameter of the circle is , find the area of the shaded region.

Possible Answers:

Correct answer:

Explanation:

2

From the given image, you should notice that the base of the triangle is also the diameter of the circle. In addition, the height of the triangle is also the radius of the circle.

Thus, we can find the area of the triangle.

Next, recall how to find the area of a circle.

To find the area of the shaded region, subtract the two areas.

Make sure to round to  places after the decimal.

Example Question #1 : How To Find The Area Of An Acute / Obtuse Isosceles Triangle

An isosceles triangle is placed in a circle as shown by the figure below.

1

If the diameter of the circle is , find the area of the shaded region.

Possible Answers:

Correct answer:

Explanation:

2

From the given image, you should notice that the base of the triangle is also the diameter of the circle. In addition, the height of the triangle is also the radius of the circle.

Thus, we can find the area of the triangle.

Next, recall how to find the area of a circle.

To find the area of the shaded region, subtract the two areas.

Make sure to round to  places after the decimal.

Example Question #21 : Triangles

An isosceles triangle is placed in a circle as shown by the figure below.

1

If the diameter of the circle is , find the area of the shaded region.

Possible Answers:

Correct answer:

Explanation:

2

From the given image, you should notice that the base of the triangle is also the diameter of the circle. In addition, the height of the triangle is also the radius of the circle.

Thus, we can find the area of the triangle.

Next, recall how to find the area of a circle.

To find the area of the shaded region, subtract the two areas.

Make sure to round to  places after the decimal.

Example Question #22 : Triangles

An isosceles triangle is placed in a circle as shown by the figure below.

1

If the diameter of the circle is , find the area of the shaded region.

Possible Answers:

Correct answer:

Explanation:

2

From the given image, you should notice that the base of the triangle is also the diameter of the circle. In addition, the height of the triangle is also the radius of the circle.

Thus, we can find the area of the triangle.

Next, recall how to find the area of a circle.

To find the area of the shaded region, subtract the two areas.

Make sure to round to  places after the decimal.

Example Question #23 : Triangles

An isosceles triangle is placed in a circle as shown by the figure below.

1

If the diameter of the circle is , find the area of the shaded region.

Possible Answers:

Correct answer:

Explanation:

2

From the given image, you should notice that the base of the triangle is also the diameter of the circle. In addition, the height of the triangle is also the radius of the circle.

Thus, we can find the area of the triangle.

Next, recall how to find the area of a circle.

To find the area of the shaded region, subtract the two areas.

Make sure to round to  places after the decimal.

Example Question #461 : Intermediate Geometry

A triangle is placed in a parallelogram so that they share a base.

9

If the height of the triangle is half the height of the parallelogram, find the area of the shaded region.

Possible Answers:

Correct answer:

Explanation:

13

In order to find the area of the shaded region, we will need to find the areas of the triangle and of the parallelogram.

First, recall how to find the area of a parallelogram.

Next, recall how to find the area of a triangle.

Now, find the height of the triangle.

Plug this value in to find the area of the triangle.

Subtract the two areas to find the area of the shaded region.

Example Question #25 : Triangles

Parallel 2

Refer to the above diagram. .

True or false: From the information given, it follows that .

Possible Answers:

False

True

Correct answer:

True

Explanation:

By the Angle-Angle Similarity Postulate, if two pairs of corresponding angles of a triangle are congruent, the triangles themselves are similar. 

 and  are a pair of vertical angles, having the same vertex and having sides opposite each other. As such, .

 and  are alternating interior angles formed by two parallel lines  and  cut by a transversal . As a consequence, .

The conditions of the Angle-Angle Similarity Postulate are satisfied, and it holds that .

Example Question #1 : How To Find If Of Acute / Obtuse Isosceles Triangle Are Similar

Parallel 2

Refer to the above diagram. .

True or false: From the information given, it follows that .

Possible Answers:

False

True

Correct answer:

False

Explanation:

The given information is actually inconclusive.

By the Angle-Angle Similarity Postulate, if two pairs of corresponding angles of a triangle are congruent, the triangles themselves are similar. Therefore, we seek to prove two of the following three angle congruence statements:

 and  are a pair of vertical angles, having the same vertex and having sides opposite each other. As such, 

, but this is not one of the statements we need to prove. Also, without further information - for example, whether  and  are parallel, which is not given to us - we have no way to prove either of the other two necessary statements. 

The correct response is "false".

Example Question #27 : Triangles

 and  are both isosceles triangles;

True or false: from the given information, it follows that .

Possible Answers:

True

False

Correct answer:

False

Explanation:

As we are establishing whether or not , then , and  correspond respectively to , and .

 is an isosceles triangle, so it must have two congruent angles.  has measure , so either  has this measure,  has this measure, or . If we examine the second case, it immediately follows that . One condition of the similarity of triangles is that all pairs of corresponding angles be congruent; since there is at least one case that violates this condition, it does not necessarily follow that  . This makes the correct response "false".

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