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Find sum of first 10 terms of an AP whose first term is minus 5 and third term is 5

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Answer:

Step By Step Explanation:

Given:

  • First term, a₁ = -5
  • Third term, a₃ = 5

To Find:

  • Sum of first 10 terms.

Now, firstly we will find common difference,

We know that,

=> a₃ = a + 2d

=> 5 = -5 + 2d

=> 10 = 2d

=> d = 10/2

=> d = 5

Hence, common difference = 5

Now, we will come calculate sum of first 10 terms.

=> Sn = n/2[2a + (n - 1)d]

=> S₁₀ = 10/2[-10 + (10 - 1)5]

=> S₁₀ = 5[-10 + 45]

=> S₁₀ = 5[35]

=> S₁₀ = 175

Hence, sum of first 10 terms = 175.


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