Class 10 Math All topics Arithmetic Progressions

If the first term of an AP is $5$ and the common difference is $−2,$ then the sum of the first $6$ terms is

(a)

$0$

(b)

$5$

(c)

$6$

(d)

$15$

Correct answer: (a)

Solution: Sum of an AP is: $2n ×[2a+(n−1)d]$

$a=5,d=−2,n=6$

Sum $=26 ×[(2×5)+(6−1)×(−2)]$

$=3×(10−10)$

$=0$

$a=5,d=−2,n=6$

Sum $=26 ×[(2×5)+(6−1)×(−2)]$

$=3×(10−10)$

$=0$

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