Question

find the sum of the first 20th term of the AP -9,-4,1
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Answer 1

Answer:

I don't know I don't know I don't know

Answer 2

Step-by-step explanation:

Given :-

AP :- -9 , -4 , 1

We have

First term (a) = -9

Common difference (d) = -4 - (-9)

• -4 + 9
• 5

We know

${S}_{n}$ = $\frac{n}{2}$[2a + (n - 1) d]

• $\frac{20}{2}$[2(-9) + (20 - 1) 5]

• 10 [(-18) + 19*5]
• 10 [(-18) + 95]
• 10 × 77
• 770

${S}_{20}$ = 770 ☑️