## Lines and Angles - ESSENTIAL POINTS

• Complementary angles - two angles whose sum is 90°.
• Supplementary angles - two angles whose sum is 180°.
• Adjacent angles - Two angles having a common vertex, a common arm and their non-common arms are on different sides of the common arm.
• Linear pair - If the non-common arms of adjacent angles form a line, they are called a Linear pair.
• Vertically opposite angles - when two lines intersect each other, they form Vertically opposite angles
• If a ray stands on a line, then the sum of the two adjacent angles so formed is 180° and vice-versa.
• If two lines intersect each other, then the vertically opposite angles are equal.
• If a transversal intersects two parallel lines, then
• corresponding angles are equal
• alternate interior angles are equal
• each pair of interior angles on the same side of the transversal are supplementary.
• If a transversal intersects two lines such that, either
• any one pair of corresponding angles is equal
• any one pair of alternate interior angles is equal
• any one pair of interior angles on the same side of the transversal is supplementary, then the lines are parallel.
• Lines which are parallel to a given line are parallel to each other.
• The sum of the three angles of a triangle is 180°.
• If a side of a triangle is produced, the exterior angle so formed is equal to the sum of the two interior opposite angles