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make a conjecture about the sum of the first 30 positive even numbers. 

2

=

2

=

1 · 22 + 4

=

6

=

2 · 32 + 4 + 6

=

12

=

3 · 42 + 4 + 6 + 8

=

20

=

4 · 52 + 4 + 6 + 8 + 10

=

30

=

5 · 6

 May 10, 2018
 #1
avatar+971 
+2

To find 30n we use formula

 

Sn=n/2⋅(2a1+(n−1)⋅d)

 

In this example we have a1=2 , d=2 , n=30. After substituting these values into the above equation, we

 

obtain:

 

S30  = 930

 

i hope this helped,

 

gavin

 May 10, 2018
edited by GYanggg  May 10, 2018

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