Question

It is given that 38, 35, 32,... is an arithmetic sequence. Mandy claims that there are 14 positive terms in the sequence. Do you agree? Explain your answer.

Collected in the board: Arithmetic sequence

Steven Zheng posted 2 months ago


Answer

Since the sequence 38, 35, 32, … is an arithmetic sequence, it is obvious from the given terms that the 1st term a_1=38, the common difference d=-3.

Apply the formula for the general terms of an arithmetic sequence

a_n=a_1+(n-1)d

If a_n>0

a_1+(n-1)d>0

38+(n-1)(-3)>0

-3n+3 >-38

3n<41

n<13\dfrac{2}{3}

Therefore, what Mandy claims is not correct. There are 13 positive terms.

Steven Zheng posted 2 weeks ago

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