Question

If the 5th and 11th terms of an A.P.be 41 and 20, then find its first term
and the sum of first 11 terms.

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Answer 1

❥︎ Answer࿐

given : a+4d=41 equation (1)

a+ 10d=20 equation (2)

to find: a=¿ and s(11) sum of 11 terms

solution࿐

solving equation (1) and (2)

a+4d=41

a+ 10d=20

-6d= 21

now d= -21/6

put value of d in equation (1)

a+4d=41

a+4*-21/6=41

a-14=41

a=41+14

a= 55

hence first term is 55

sum of 11 terms

formula

s(n)=n/2(2a+(n-1)*d

s(11)=11/2(2*55+(11-1)*-21/6

s(11)=11/2(110-35)

s(11)=11/2(75)

s(11)=825/2

hence sum of 11 term is 825/2 and first term of ap is 55

Thanks

hope its helpful

Answer 2

Please refer to the following attachment and if possible mark me as brainliest.....