Concept 1 Sum of angles on a straight line is 180∘ Angle SRP+ Angle PRS=180 Angle SRP+2x−10=180 Angle SRP=180−2x+10 Angle SRP =180+10−2x Angle SRP=190−2x Concept 2 The interior angles of equilateral triangle are the same. Angle SRP= Angle RPQ= Angle PQR=190−2x Concept 3 The sum of interior angles of a triangle gives 180∘ Angle SRP+ Angle RPQ+ Angle PQR=180 (190−2x)+(190−2x)+(190−2x)=180 3x(190−2x)=180 Divide both sides by 3 190−2x=
180
3
190−2x=60 −2x=60−190 −2x=−130 Divide both sides by -2