Find the sum of first 17terms of an AP whose 4th and 9th term are - 15

1.	Find the sum of first 17terms of an AP whose 4th and 9th term are - 15and -30 respectively
Answer» Answer: -510 Step-by-step explanation: Let a & d be the FIRST term and COMMON DIFFERENCE of the A.P. 4th term = a + 3D = -15 9th term = a + 8d = -30 Solving above two EQUATIONS we have a = -6, d = -3 Than the sum of first 17 terms is given by, S = n/2 { 2a + (n -1)d} = 17/2 { 2 * (-6) + (17-1)(-3) } S = -510

Find the sum of first 17terms of an AP whose 4th and 9th term are - 15and -30 respectively

Answer»

Answer:

-510

Step-by-step explanation:

Let a & d be the FIRST term and COMMON DIFFERENCE of the A.P.

4th term = a + 3D = -15

9th term = a + 8d = -30

Solving above two EQUATIONS we have

a = -6, d = -3

Than the sum of first 17 terms is given by,

S = n/2 { 2a + (n -1)d} = 17/2 { 2 * (-6) + (17-1)(-3) }

S = -510

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Find the sum of first 17terms of an AP whose 4th and 9th term are - 15and -30 respectively

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