Chapter 1: Problem 7
Use a compass and a straightedge to complete the constructions. Given: \(\quad\) Line \(\ell\) containing point \(A\) Construct: \(A 45^{\circ}\) angle with vertex at \(A\) GRAPH CAN'T COPY
Short Answer
Expert verified
Draw a perpendicular and bisect it to form a 45° angle.
Step by step solution
01
Draw a Ray from Point A
Begin by placing the compass point on point \( A \) and drawing an arc that intersects line \( \ell \) at some point. This will mark a point on ray \( AB \). This ray will be one side of your 45° angle.
02
Construct a 90° Angle
From point \( A \), keep the same compass width and draw another arc that intersects ray \( AB \) at a new point, \( C \). Now draw an arc from point \( C \) that intersects the previous arc at a point \( D \). Without changing the compass width, repeat from \( D \) and find intersection \( E \). Draw a ray from \( A \) through \( E \) which will be perpendicular to line \( \ell \).
03
Bisect the 90° Angle to Create a 45° Angle
Place the compass at point \( C \) and adjust it to span beyond half the distance from \( C \) to \( E \). Swing an arc into the interior of the angle. Without changing the width, repeat the arc from point \( E \). The two arcs intersect at point \( F \). Draw a ray from point \( A \) through point \( F \), which will form a 45° angle with ray \( AB \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Compass and Straightedge
Geometry constructions often rely on the use of two simple tools: the compass and the straightedge. These instruments help us draw accurate shapes and angles without measuring devices.
- The compass is used to draw arcs and circles, helping us mark important points in our construction.
- The straightedge, which can be a ruler without measurement markings, helps in drawing straight lines or rays.
Perpendicular Bisector
A perpendicular bisector is a line that divides another line segment into two equal parts at a 90-degree angle. Creating a perpendicular bisector is a common task in geometry, and it serves as a fundamental step in constructing angles.
Here’s how you can construct a perpendicular bisector:
Here’s how you can construct a perpendicular bisector:
- Place the compass point on one end of the segment and draw an arc that is more than half the length of the segment.
- Without changing the compass width, draw another arc from the other end of the segment. The intersections of these arcs are the points you'll use to draw the bisector.
- Connect these intersection points using a straightedge. This forms the perpendicular bisector.
Angle Bisector
An angle bisector is a ray that divides an angle into two equal parts. This concept is crucial in constructing specific angles from a given angle.
To accurately bisect an angle:
To accurately bisect an angle:
- Place the compass at the vertex of the angle and draw an arc that crosses both sides of the angle.
- From those intersection points, draw arcs within the angle that meet; mark this new intersection point.
- Use a straightedge to draw a line from the vertex through this intersection point, creating two equal angles.
90-Degree Angle Construction
Constructing a 90-degree angle is a fundamental skill in geometry and is often accomplished through the use of a compass and straightedge.
To construct a 90-degree angle:
To construct a 90-degree angle:
- Select a base line and mark a starting point.
- From this point, use a compass set to a comfortable width and draw an arc that intersects the base line.
- With the same compass width, without changing it, draw arcs from each intersection point on the line.
- These arcs will meet at a new point, and drawing a line through this point and the initial point creates a perpendicular to the base line.