The Total solution for NCERT class 6-12
In ╬ФDOC and ╬ФBOA,
AB || CD, thus alternate interior angles willbe equal,
тИ┤тИаCDO = тИаABO
Similarly,тИаDCO = тИаBAO
Also, for the two triangles ╬ФDOC and ╬ФBOA,vertically opposite angles will be equal;тИ┤тИаDOC = тИаBOA
Hence, by AAA similarity criterion,╬ФDOC ~ ╬ФBOA
Thus, the corresponding sides areproportional.
DO/BO = OC/OA
тЗТOA/OC = OB/OD
Hence, proved.