sum of first n even numbers

Even numbers are 2,4,6,8,10,….

Now we will see the sum of elements:

Sum of first 2 even numbers: 2+4= 6= 2(2+1)

Sum of first 3 even numbers: 2+4+6= 12= 3(3+1)

Sum of first 4 even  numbers: 2+4+6+8=20= 4(4+1)

Sum of first 5 even numbers: 2+4+6+8+10 = 30 = 5(5+1)

Sum of first n even numbers: 2+4+6+8+10+. . . . .  n numbers= n(n+1)

since the sum of first n even numbers is n(n+1)

see also:Average of first n even numbers