Question

Find the sum (a) . 5+(-2)+(-5)

Answer 1

Step-by-step explanation:

Answer

From the given series

a=1,a

n

=−236

d

1

=−2−1=−3

d

2

=−5−(−2)=−5+2=−3

d

3

=−8−(−5)=−3

∴d=d

1

=d

2

=d

3

=−3

Now, a+(n−1)d=a

n

⇒1+(n−1)(−3)=−236

⇒−3(n−1)=−236−1

⇒−(n−1)=

3

−237

⇒n−1=+79

⇒n=80

Now, S

n

=

2

n

[a+a

n

]

s

80

=

2

80

[1+(−236)]

=−9400

Hence, the sum of all terms = -9400