Page 173 - ICSE Math 7

¾ Two angles are called adjacent angles if they have a common vertex, a common arm and the
other arms are on the opposite sides of the common arm.
¾ If the sum of the magnitudes of two adjacent angles is 180°, then they are known as a linear pair.
¾ When two lines intersect at a point, then the angles on the opposite sides of the point of intersection
are known as vertically opposite angles.
¾ Transversal is a line which intersects two or more lines at distinct points.
¾ If two straight lines intersect, then the sum of each pair of adjacent angles is supplementary and
vertically opposite angles are equal.
¾ If two parallel lines are intersected by a transversal, then
(a) the alternate angles are equal,
(b) the corresponding angles are equal, and
(c) the interior angles on the same side of the transversal are supplementary.
¾ If two straight lines are cut by a transversal, then the lines are parallel if:
(a) a pair of alternate angles are equal, or
(b) a pair of corresponding angles are equal, or
(c) the interior angles on the same side of the transversal are supplementary.

MENTAL MATHS

1. Write True or False.
(a) A plane consists of finite number of points and lines.
(b) The distance between two parallel lines always remains the same.

(c) The point of intersection of two lines is known as the point of concurrence.
(d) One and only one line can pass through a point.
(e) Four points are collinear if at least three of them lie on the same line.
(f) Two rays having the same initial point form an angle.
2. Fill in the blanks.
(a) The complement of 60° is ____________.
(b) The supplement of 170° is ____________.
(c) In the adjoining figure, if x = y = z then x = ____________. z y
(d) Vertically opposite angles are always ____________. x

(e) If the sum of two adjacent angles is 180°, then they form a ____________.
(f) If one of the angles forming a linear pair is an acute angle, then the other angle is ____________.

PRACTICE TIME

1. For the following figures, find angle x.

x + 20°
(a) (b) (c) x + 15°
68° x + 40°
x x
x°

159