Notice that . Solve for .
A geometric progression has first term and common ratio . The sum of the first three terms is and the sum to infinity is .
Find the values of and .
------(1)
------(2)
(2)-(1):
-----(3)
From (2), -----(4)
Sub (4) into (3):
I understand why i have to reject and . But i don't understand why is rejected too