Answer
Reason | Abbreviation |
Vertically opposite angles are equal | vert opp Ðs |
Adjacent angles on a straight line add to 180º | Adj, Ðs on str. line |
Angles at a point add to 360º | Ðs at pt |
Angles in a triangle add to 180º | Ð sum of Δ |
The exterior angle of a triangle equals the sum of the two interior opposite angles | ext Ð of Δ |
The base angles of an isosceles triangle are equal | base Ðs isos. Δ |
The angle sum of an isosceles triangle is 180º | Ð sum isos. Δ |
Each angle in an equilateral triangle is 60º | Ð in equilat. Δ |
Corresponding angles on parallel lines are equal | corresp Ðs, // lines |
Alternate angles on parallel lines are equal | alt. Ðs, // lines |
Co-interior angles on parallel lines are supplementary (add to 180º) | co-int Ðs, // lines |
The interior angles of a polygon add to 180(n – 2)º, where n is the number of sides | int Ð sum of polygon |
The exterior angles of a polygon add to 360 | ext Ð sum of polygon |
Isosceles triangle, equal radii | isos Δ, = radii |
Angles of isosceles triangle add to 180º , equal radii | Ð sum isos Δ, = radii |
Base angles of isosceles triangle are equal, equal radii | base Ðs, isos Δ, = radii |
The angle at the centre is equal to twice the angle at the circumference on the same arc | Ð at centre |
Angles on the same arc are equal | Ðs on same arc |
The angle in a semicircle is a right angle | Ð in semicircle |
Opposite angle of a cyclic quadrilateral are supplementary (add to 180º) | opp Ðs, cyclic quad |
The exterior angle of a cyclic quadrilateral is equal to the interior opposite angle | ext Ð, cyclic quad |
The perpendicular from the centre to the chord bisects the chord | from centre to chord |
The angle where the radius meets the tangent is 90º | tgt rad |
Tangents from a point to a circle are the same length | equal tangents |