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Question
The first term of an A. P. is 5 and the common difference is 4. Complete the following activity and find the sum of the first 12 terms of the A. P.
a = 5, d = 4, s12 = ?
`s_n = n/2 [ square ]`
`s_12 = 12/2 [10 +square]`
`= 6 × square `
` =square`
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Solution
`s_n = n/2 [ 2a +(n-1)d ]`
`s_12 = 12/2 [10 + 11 xx 4 ]`
` =12/2[10+44]`
`= 6 ×54 `
` s_n= 324`
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