B–2
Name
Date
Prove It!
Draw intersecting lines AB and CD. Have them intersect at point X.
Use your protractor to complete the following statements.
• Adjacent angles AXC and DXA add up to
.
• Adjacent angles AXD and DXB add up to
.
• Opposite angles AXC and BXD have the same measurement:
.
• Opposite angles AXD and BXC have the same measurement:
.
Copyright © Houghton Mifflin Company. All rights reserved.
• The total measurement of all four angles formed by the intersecting lines is
.
1.
Why are the first two statements true for all intersecting lines? (Think: What kind
of angle is equal to 180°?)
2.
Picture two intersecting lines that are perpendicular. What is true of the measurements of
all four angles they form?
3.
Use a compass to draw a circle with midpoint X. Divide the circle into angles by drawing
two intersecting lines that are perpendicular. What must the total measurement of all the
angles in the circle be? Explain.
B–2
Name
Date
Prove It!
Draw intersecting lines AB and CD. Have them intersect at point X.
Drawings will vary.
Check students’
drawings.
D
A
X
C
B
Use your protractor to complete the following statements.
• Adjacent angles AXC and DXA add up to
180°
.
• Adjacent angles AXD and DXB add up to
180°
.
• Opposite angles AXC and BXD have the same measurement:
Answers will
vary.
.
• Opposite angles AXD and BXC have the same measurement:
Answers will
vary.
.
• The total measurement of all four angles formed by the intersecting lines is
Copyright © Houghton Mifflin Company. All rights reserved.
1.
360°
.
Why are the first two statements true for all intersecting lines? (Think: What kind
of angle is equal to 180°?)
Any two intersecting lines form a straight angle.
2.
Picture two intersecting lines that are perpendicular. What is true of the measurements of
all four angles they form?
Angles each measure 90°
3.
Use a compass to draw a circle with midpoint X. Divide the circle into angles by drawing
two intersecting lines that are perpendicular. What must the total measurement of all the
angles in the circle be? Explain.
360°; the measurement of angles in the circle must equal
the measurement of all four angles formed by the two
intersecting lines.