This question was asked in Ex 7.2, 12
After add and sub of 1 where from in place of 1 t-1 came....... Say immediately.. Please..... Say.... 
MahalakshmiVinayagam MahalakshmiVinayagam's image
MahalakshmiVinayagam MahalakshmiVinayagam
Nov. 12, 2019, 6:32 p.m.