HGello, Tweety!
The first three terms are: .The first three terms of an arithmetic sequence are: .
where is acute. . Find the value of
We have: .
Subtract [2] from [1]: .
Subtract [3] from [2]: .
Equate [4] and [5]: . .
Divide by 2: .
Since
. . we have: .
. . . That is: .
Therefore: .