Question

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.

Answer 1

`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`