1.

Find the sum of (-20 )and 68​

Answer»

ong>Answer:

We have:

2

+

9

+

16

+

23

+

30

+

...

This is an arithmetic series, so LET's DETERMINE the common difference

d

:

⇒

d

=

u

2

−

u

1

⇒

d

=

9

−

2

⇒

d

=

7

Then, let's use the formula for the sum of

n

TERMS of an arithmetic sequence:

⇒

S

n

=

n

2

(

2

u

1

+

(

n

−

1

)

d

)

Then, for the first

68

terms of the series:

⇒

S

68

=

68

2

(

2

⋅

2

+

(

68

−

1

)

7

)

⇒

S

68

=

34

(

4

+

67

⋅

7

)

⇒

S

68

=

34

(

4

+

469

)

⇒

S

68

=

34

(

473

)

⇒

S

68

=

16

,

082


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