How do you find the sum of the arithmetic sequence having the data given #a_1=5#, d = -2, n = 12?

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Answer 1 · 2016-02-22T18:56:55

The sum:
#S_12 = -72#

The first term: #a_1=5#

The common difference: #d=-2#

Number of terms of the sequence: #n=12#

The sum of #n # terms of arithmetic sequence is found using formula:

#S_n = n/2 [2a + (n-1)d]#

#S_n = 12/2 [2 xx 5 + (12 -1) xx -2]#

# = 6 [10 + (11) xx -2]#

# = 6 [10 -22 ]#

# = 6 xx -12#

#S_12 = -72#