Difference AP

Calculate the difference of arithmetic progression if the sum of its first 19 members Sn = 8075 and the first member is a1 = 20

Correct result:

d =  45

Solution:

S=na1+an2 8075=1920+20+(19−1)d2 850=2⋅20+(19−1)d 810=18d d=45 S=20+65+110+155+200+245+290+335+380+425+470+515+560+605+650+695+740+785+830=8075

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