The sum of the 1st n terms of an ap is 5n*2+3n.if its mth term is 168 find the value of m
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Sum of n terms = 5n²+3n .
First term = 5(1²)+3(1) = 8 .
Sum of two terms = 5(2²)+3(2) = 5(4)+ 6 = 26 .
Second term = 26 - 8 = 18 .
Common difference = 18 - 8 = 10 .
We know that
mth term = 168
8 + ( m - 1 ) 10 = 168
m - 1 = 16
m = 17
First term = 5(1²)+3(1) = 8 .
Sum of two terms = 5(2²)+3(2) = 5(4)+ 6 = 26 .
Second term = 26 - 8 = 18 .
Common difference = 18 - 8 = 10 .
We know that
mth term = 168
8 + ( m - 1 ) 10 = 168
m - 1 = 16
m = 17
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