In these lessons, we look at geometry word problems, which involves geometric figures and angles described in words. You would need to be familiar with the formulas in geometry.
Related Pages
Perimeter and Area of Polygons
Nets Of 3D Shapes
Surface Area Formulas
Volume Formulas
More Geometry Lessons
Making a sketch of the geometric figure is often helpful.
You can see how to solve geometry word problems in the following examples:
Problems involving Perimeter
Problems involving Area
Problems involving Angles
There is also an example of a geometry word problem that uses similar triangles.
Example 1:
A triangle has a perimeter of 50. If 2 of its sides are equal and the third side is 5
more than the equal sides, what is the length of the third side?
Solution:
Step 1: Assign variables:
Let x = length of the equal side.
Sketch the figure.
Step 2: Write out the formula for
perimeter of triangle.
P = sum of the three sides
Step 3: Plug in the values
from the question and from the sketch.
50 = x + x + x + 5
Combine like terms
50 = 3x + 5
Isolate variable x
3x = 50 – 5
3x = 45
x =15
Be careful! The question
requires the length of the third side.
The length of third side = 15 + 5 =20
Answer: The length of third side is 20
Example 2:
Writing an equation and finding the dimensions of a rectangle knowing the perimeter and
some information about the about the length and width.
The width of a rectangle is 3 feet less than its length. The
perimeter of the rectangle is 110 feet. Find its dimensions.
Example 1:
A rectangle is 4 times as long as it is wide. If the length is increased by 4 inches and
the width is decreased by 1 inch, the area will be 60 square inches. What were the
dimensions of the original rectangle?
Solution:
Step 1: Assign variables:
Let x = original width of rectangle
Sketch the figure
Step 2: Write out the formula for area of rectangle.
A = lw
Step 3: Plug in the values from the question and from the sketch.
60 = (4x + 4)(x –1)
Use distributive property to remove brackets
60 = 4x^{2} – 4x + 4x – 4
Put in Quadratic Form
4x^{2} – 4 – 60 = 0
4x^{2} – 64 = 0
This quadratic can be rewritten as a difference of two squares
(2x)^{2} – (8)^{2} = 0
Factorize difference of two squares">
(2x)^{2} – (8)^{2} = 0
(2x – 8)(2x + 8) = 0
We get two values for x.
Since x is a dimension, it would be positive. So, we take x = 4
The question requires the dimensions of the original rectangle.
The width of the original rectangle is 4.
The length is 4 times the width = 4 × 4 = 16
Answer: The dimensions of the original rectangle are 4 and 16.
Example 2:
This is a geometry word problem that we can solve by writing an equation and factoring.
The height of a triangle is 4 inches more
than twice the length of the base. The area of the triangle is 35
square inches. Find the height of the triangle.
Example 1:
In a quadrilateral two angles are equal. The third angle is equal to the sum of the two equal angles.
The fourth angle is 60° less than twice the sum of the other three angles. Find the measures of the
angles in the quadrilateral.
Solution:
Step 1: Assign variables:
Let x = size of one of the two equal angles
Sketch the figure
Step 2: Write down the
sum of angles in quadrilateral.
The sum of angles in a quadrilateral is 360°
Step 3: Plug in the values from the question and from the sketch.
360 = x + x + (x + x) + 2(x + x + x + x) – 60
Combine like terms
360 = 4x + 2(4x) – 60
360 = 4x + 8x – 60
360 = 12x – 60
Isolate variable x
12x = 420
x = 35
The question requires the values of all the angles.
Substituting x for 35, you will get: 35, 35, 70, 220
Answer: The values of the angles are 35°, 35°, 70° and 220°.
Example 2:
The sum of the supplement and the complement of an angle is 130 degrees. Find the measure of the angle.
Indirect Measurement Using Similar Triangles
This video illustrates how to use the properties of similar triangles to determine the height of a tree.
How to solve problems involving Similar Triangles and Proportions?
Examples:
Given that triangle ABC is similar to triangle DEF, solve for x and y.
The extendable ramp shown below is used to move crates of fruit to loading docks of different heights.
When the horizontal distance AB is 4 feet, the height of the loading dock, BC, is 2 feet. What is the height of the loading dock, DE?
Triangles ABC and A’B’C' are similar figures. Find the length AB.
How to use similar triangles to solve a geometry word problem?
Examples:
Raul is 6 ft tall and he notices that he casts a shadow that’s 5 ft long. He then measures
that the shadow cast by his school building is 30 ft long. How tall is the building?
Try the free Mathway calculator and
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