Question

the nth term of an ap is given by -4n + 15. find the sum of first 20 terms of this ap.
plz answer !!!!!​

Answer 1

Answer:

n= -4n+15

putting the value

20= -4n +15

20-15= -4n

5=-4n

5upon-4=n

Step-by-step explanation:

it may help you

Answer 2

Answer:

-540

Step-by-step explanation:

for n = 1 Tn = 11

for n = 2 Tn = 8

so a = 11 d = -4

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

10[22+19(-4)]

10[22-76]

10[-54]

-540

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