S20=n/2(A1+A5)
-420=5/2(10+A5)
-420=2.5(10+A5)
-420=25+2.5A5
-420-25=2.5A5
-445=2.5A5
-178=A5
A1=10 A5=-178 d=?
d=An-A1/n-1
d=-178-10/5-1
d=-188/4
d=-47
Thus, the first 5 terms are 10, -37, -84, -131, -178.
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Answers & Comments
S20=n/2(A1+A5)
-420=5/2(10+A5)
-420=2.5(10+A5)
-420=25+2.5A5
-420-25=2.5A5
-445=2.5A5
-178=A5
A1=10 A5=-178 d=?
d=An-A1/n-1
d=-178-10/5-1
d=-188/4
d=-47
Thus, the first 5 terms are 10, -37, -84, -131, -178.