Calculate the angle x

MathematicsGeometryMedium

Published:

Work out the size of angle $x$.

This question includes visual content: The image shows a geometric diagram consisting of two parallel lines intersected by two transversals that form a triangle. An angle of 85° is at the top vertex, an angle of 42° is at the bottom-left intersection, an angle of 34° is at the bottom-right vertex of the triangle, and the angle x is at the intersection point of the second transversal and the bottom base line.

Animated Video Solution

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Step by Step Written Solution

1
Step 1

Hi Halimah, let's solve this geometry problem together. We need to find the value of angle x.

Finding Angle $x$

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Step 2

First, let's look at the diagram. We have a set of parallel lines, indicated by the arrows. We also see several triangles and known angles: 85 degrees, 42 degrees, and 34 degrees.


Given:

* Parallel lines (marked with arrows)

* Angles: $85^\circ, 42^\circ, 34^\circ$

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Step 3

Let's focus on the largest triangle containing the 34 degree and 85 degree angles. If we can find the third angle of this big triangle, it will help us use properties of parallel lines.

85°34°
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Step 4

Wait, a better approach is to look at the relative positions. Notice the parallel lines creating corresponding or alternate angles.

$$Exterior\ Angle\ Theorem?$$
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Step 5

Actually, let's look at the smaller triangle on the left. It has an interior angle of 42 degrees. Because the two vertical-ish lines are parallel, we can use the corresponding angle property.

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Step 6

Let's focus on the triangle with the 85 degree and 34 degree corners. Let's call the bottom left vertex of the whole figure Angle A. In the largest triangle, the sum of angles must be 180 degrees.

$$85^\circ + 34^\circ + \text{Angle A} = 180^\circ$$
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Step 7

Adding 85 and 34 gives us 119.

$$119^\circ + \text{Angle A} = 180^\circ$$
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Step 8

Subtracting 119 from 180, we find that Angle A is 61 degrees.

$$\text{Angle A} = 61^\circ$$
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Step 9

Now, look at the triangle formed by the first parallel line. It has angles of 42 degrees and our newly found 61 degrees. Let's find the third angle in that triangle, which I'll mark at the top intersection.

Small Triangle Analysis

$$61^\circ + 42^\circ + \text{Top Angle} = 180^\circ$$
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Step 10

61 plus 42 equals 103. Subtracting that from 180 gives us 77 degrees for that top intersection.

$$180^\circ - 103^\circ = 77^\circ$$
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Step 11

Now consider the parallel lines. Angle x is an exterior angle to a triangle, or we can use corresponding angles. Notice that the angle corresponding to x is the sum of the top angle and the 85 degree angle. Let's try a simpler path.

Alternate Path

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Step 12

Look at the triangle containing angle x as an exterior angle. In geometry, the exterior angle of a triangle is equal to the sum of the two opposite interior angles.

$$x = \text{Angle 1} + \text{Angle 2}$$

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About This Question

Subject
Mathematics
Topic
Geometry
Difficulty
Medium
Question Type
Open Ended

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