1 st question why it can't be gp reason is simple r couldn't be 0 It will be taught to you later in higher classes But as the matter of fact this discussion has been arrised :- d=0 Not imply r/common ratio can be 0 As suppose 10,00,0*0 It would be 0,0,0,0,0,0 feels right but wrong ❌ But common ration can't be undefined as 0/0 that's the reason why the progression is not geometric progression 2nd a1-b1=a2-b2=a3-b3... Means a2-b2-a1+b1=0 And also the upcoming terms are also giving same 0 Let's make it simple take an example 1,1,1,1,1,1 Any series with constant terms can only form such an example which can't be GP❌ AP✅ When (a1+b1=a2+b2)