find the sum of first 15 term of an A.P -1, -5, -9..........
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Sum of First 15 terms = -435
Step-by-step explanation:
By using formula : S = n/2{ 2a + (n-1)d}
S = 15/2 { 2(-1) + (15-1)(-4)}
S = 15/2 { -2 - 56 }
S = 15/2 { -58}
S = 15 × (-29)
S = -435
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