Its an indirect proof, so 3 steps :-
1) you start with the opposite of wat u need to prove
2) arrive at a contradiction
3) concludeReport · 29/6/2015261
since you wanto prove 'diagonals of a parallelogram bisect each other', you start wid the opposite of above statement, like below :- step1 : Since we want to prove 'diagonals of a parallelogram bisect each other', lets start by assuming the opposite, that the diagonals of parallelogram dont bisect each other.Report · 29/6/2015261

Since, we assumed that the diagonals dont bisect each other,
OC≠OA
OD≠OBReport · 29/6/2015261
Since, OC≠OA, △OAD is not congruent to △OCBReport · 29/6/2015261

∠AOD≅∠BOC as they are vertical angles,
∠OAD≅∠OCB they are alternate interior angles
AD≅BC, by definition of parallelogram
so, by AAS, △OAD is congruent to △OCBReport · 29/6/2015261
But, thats a contradiction as we have previously established that those triangles are congruentReport · 29/6/2015261
step3 :
since we arrived at a contradiction, our assumption is wrong. so, the opposite of our assumption must be correct. so diagonals of parallelogram bisect each other.

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