what is the twentieth term of the arithmetic sequence 21, 18, 15, 12, ?

78

-39

-36

1

Option (C).

The twentieth term of the given arithmetic sequence is -36.

Step-by-step explanation:

The given arithmetic sequence is,

21, 18, 15, 12, ...........

Now, the first term of the arithmetic sequence, a₁ = 21

Second term of the arithmetic sequence, a₂ = 18

Third term of the arithmetic sequence, a₃ = 15

Fourth term of the arithmetic sequence, a₄ = 12

and so on.

Now, common difference, d = a₂ - a₁ = 18 - 21 = -3

We know that, term of an arithmetic sequence is given by,

aₙ = a₁ + (n - 1)d

To find the term of the given arithmetic sequence, we will substitute the values of a₁ , n and d in the above expression of aₙ.

Put a₁ = 21; n = 20 and d = -3 in the above expression of aₙ, we get

So, twentieth term of the given arithmetic sequence is -36.

Hence, option (C) is the correct answer.

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step-by-step explanation:

in the attachment.   i didn't see your choices.   the word which means there is choices.

step-by-step explanation:

(x,y)

x tells you how much left or right you go from the origin

y tells you how much down or up you go from the origin

so for example (-3,2), you go left 3 and up twice. i denoted which of the ordered pairs is which in my graph.