Question

find the sum of first 9 terms if an = 10 , d = 2​

Answer 1

Sum of first n terms = n/2 * (2a + (n-1)*d)

= 9/2 * (2*10 + (9-1)*2) = 9/2*(20+16) = 9/2 * 36

= 162

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Answer 2

Question;

find the sum of first 9 terms if an = 10 , d = 2​

To find;

• the sum of the first 9 terms f the Arithmetic Progression

Solution;

Given;

• first term a = 10
• common difference d = 2

• Number of terms = 9

Formula used;

the sum of n terms of an AP = n/2 * [2a + (n-1) *d]

Evaluating;

the sum of 9 terms of this AP = 9/2 * [ 2*10 + (9-1) * 2]

                                                 = 9/2 * [20 + 8 * 2]

                                                 = 9/2 * [ 20 + 16]

                                                 = 9/2 *36

                                                 = 162

Conclution;

the sum of the first 9 terms of this arithmetic progression is 162.