Which Term Of The Arithmetic Sequence Is -18 Given That A,=7 And A2=2?

Which term of the arithmetic sequence is -18 given that a,=7 and a2=2?

Answer: 6th term

Step-by-step explanation:

Get the common difference (d) first.

a_{2} - a_{1} = 2-7 = -5

Now, lets find out which term is -18.

a_{n} = a_{1} + (n-1)d\\ -18 = 7 + (n -1)(-5)\\ -18 = 7 + (-5n+5)\\ -18 = 7 -5n+5\\ -18 = -5n +12\\ -18-12 = -5n\\ -30 = -5n\\ \frac{-30}{-5} = \frac{-5n}{-5} \\ \boxed{\boxed{6 = n}}

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