MATH F1

Form 1 未教 arithmetic progression (A.P.) 不能用吧?

那麼只能用未知數x與數列的關係推算出其公式

the sequence is 3, 3+x, 3+2x, 3+3x, ...... ,3+(n-1)(x)

the 15th term = 3+(15-1)x = 31

3+14x = 31
14x = 28
x =2

the sequence is in the form of
3+(n-1)(2)

therefore the 34th term =

3+(34-1)(2)
= 3+66
= 69