If The 9th and 21st term of an A.P are 75 and 83 respectively. Find its 81st term
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If The 9th and 21st term of an A.P are 75 and 83 respectively. Find its 81st term
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Answer:
123
Step-by-step explanation:
let a be the first term and d be the common difference:
given:
a+8d= 75 and a+20d= 83
therefore, a= 75-8d and a= 83-20d
so, 75-8d= 83-20d
or, 20d-8d= 83-75
or, 12d= 8
so, d= 8/12= 2/3
thus, a= 75-8(2/3)= 209/3
hence, 81st term = a+ 80d = 209/3+ 80(2/3) = 369/3
therefore, 81st term = 123
Step-by-step explanation: