The sum of n terms of an AP is n^2+3n . Find its 20^th term

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Solution

Sn=n2+3n
S1=1+3
=4
a1=4
S2=4+6=10
a2=S2-S1
=10-4=6
d=a2-a1=6-4=2
a20=4+19(2)=4+38=42
a20=42

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The sum of n terms of an AP is n^2+3n . Find its 20^th term

Sn=n2+3n S1=1+3 =4 a1=4 S2=4+6=10 a2=S2-S1 =10-4=6 d=a2​-a1=6-4=2 a20=4+19(2)=4+38=42 a20=42

Sn=n2+3n
S1=1+3
=4
a1=4
S2=4+6=10
a2=S2-S1
=10-4=6
d=a2-a1=6-4=2
a20=4+19(2)=4+38=42
a20=42