Question

tq=75 t21=183 find t15​

Answer 1

Answer:

Step-by-step explanation:

let 9th term be t9 & 21st term be t21 .

tn = a+(n-1)d

t9 = a+(9-1)d

75=a+8d ----(1)

t21 = a+(21-1)d

183 = a+20d ------(2)

substracting eq(1) & (2)

we get , 12d=108

d=108/12

d=9

substituting value of d in eq(1)

75=a+8×9

75=a+72

a=75-72

a=3

therefore t81 (81st term ) is

t81=a+(81-1)d

t81= 3+80×9

t81=3+720

t81 = 723

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