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From Karnataka Open Educational Resources
Activity-construction of angles (view source)
Revision as of 05:40, 2 November 2019
, 05:40, 2 November 2019→Construction of an angle with measure 22.5∘
===Process (How to do the activity)===
===Process (How to do the activity)===
#
# Ask students which angle could be drawn with a scale? (Straight Angle)
# If we can 'halve' any angle, then we can derive angles from the straight angle - in succession, this would be as follows - ∡180∘ -> ∡90∘, ∡90∘ -> ∡45∘, ∡45∘ - > ∡22.5∘ and so on.
# Explain the process of constructing an Angle bisector using only compass (without using a protractor). Students can follow and do the construction in their books
## Draw a line segment or a line. Identify a point on this segment. We can treat this point as the vertex of a straight angle
## Construct two arcs from the vertex of the straight angle, such that each cuts the line segment on either side of the vertex.
## Plot the intersection point of each arc and the arms of the straight angle.
## From each intersection, draw an arc of same measure, such that the two arcs intersect.
## Plot the intersection point of these two arcs
## Construct a line segment (or line or ray) from the vertex to this intersection point.
## This process will create two angles. Measure both angles. They will be 90 each
## Why does this process work? (Explanation - locus of points equidistant from the two points which are equidistant from the vertex)
## Following the same process. construct the bisector of one of these two right angles. We will get two angles of 45 each
## Following the same process. construct the bisector of one of these angles, which measure 45. We will get two angles of 22.5 each
# You can use the 'Play - Construction protocol' to show the above steps one by one. But do this after constructing the bisectors using Geogebra.
===Evaluation at the end of the activity===
===Evaluation at the end of the activity===
# Ask students, what are the other angles that can drawn in the same construction. (Hint, there are new angles created, which are adjacent/ complementary / supplementary to the angles we have discussed. For eg. we get an angle with measure 135 (by considering one 90 and one 45 angles adjacent to each other).
[[Category:Lines and Angles]]
[[Category:Lines and Angles]]
[[Category:Class 9]]
[[Category:Class 9]]
