Question

21/2 [2×20+ (27-1) 2]
solve its
formula
tn = a+ (n-1) d Or
sn = n/2(a+(n-1) d) any one formula is used here but i dont know
plzz it's urgent help it​

Answer 1

Answer:

21/2*{2*20(27-1)2}

21/2*{40*26*2}

10.5*40*26*2

=21840