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Find the sum of the first 20 terms of the AP 16+9+2+(-5)+....

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a=16
d = -7
S20 = 20/2 (2*16 + 19(-7))

a=16
d=-7
S20=n/2[2a+(n-1)d]
S20=20/2[2*16+(20-1)-7]
S20=10[32-133]
S20=10(-101)
S20=-1010

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