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The first term of an A.P. is 5 and the c...

The first term of an A.P. is 5 and the common difference is 4. Complete the following activity to find the sum of first 12 terms of the A.P.

Text Solution

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`a=5, d= 4 , S_(12) = ?`
`S_(n) = ( n )/(2) [ square]` …(Formula )
`:. S_(12) = (12)/(2) [ 10 + square]` …(Substituting the values )
`= 6[ 10 + 44]`
`= 6 xx square`
`= square `
Activity `:` `a=5, d= 4, S_(12) ?` ltbr `S_(n) = ( n )/(2) [ 2a+ ( n-1)d ]`
`:.S_(12) = ( 12)/(2) [ 10+ ( 12-1) xx4]`
`= 6[10+44]` ,brgt `= 6 xx 54` ,brgt `= 324 `
`:. S_(12) = 324`
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The first term of an A.P. is 5 and the common difference is 4. Complete the following activity and find the sum of first 12 terms of the A.P. Here, a=5, d=4,S_(12)=? S_(n)=(n)/(2)[.............] thereforeS_(12)=(12)/(2)[10+..........] =6xx...............=.............

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Knowledge Check

  • The sum of first n terms of an A.P. is 5n ^(2)+ 4n, its common difference is :

    A
    9
    B
    10
    C
    3
    D
    `-4`

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