Answer:
The common difference would be calculated as:
(a21-a19)/2
(-164--(-58 ))/2 (Replacing the values )
(-164 +58)/2 (Changing signs)
(-106)/2(Subtracting)
-53
Then we are going to replace the common difference(d) in the sequence formal with the 21st term . It is done for finding the first term of the sequence.
a21=a0+d*(n-1)
-164=a0+-53*(21-1) (Replacing the values)
-164=a1-53(20) (Subtracting)
-164=a1-1060 (Multiplying )
-164+1060=a1 (Adding 1060 on both sides of the equation)
896=a1
The answer would be : an= 896-53*(n-1), which is the option B.
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