plzz.help me..the sum of first n terms of an ap..is 5n square +3n..if its mth term is 168..find the value of m also find the 20th term of this ap??
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an=sn-sa-1
an=(5n sq+3n)-(5(n-1)sq+3(n-1))
an=(5n sq+3n)-(5n sq-7n+2)
so nth term=10n-2
now mth term=168
an=(5n sq+3n)-(5(n-1)sq+3(n-1))
an=(5n sq+3n)-(5n sq-7n+2)
so nth term=10n-2
now mth term=168
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