college algebra word problem

Question

Express the description of a sum using summation notation.

The sum from n = 0

 to n = 9 of 7n

Answer 1

0+1+2+3+4+5+6+7+8+9 = 9(10)/2 = 45

Gauss' formula is n/n+1)/2 If n=9, the sum = 45

Not sure what the 7n is about. Unless you're asking to sum all integers 1 to 7(9) = 63. Then

the sum = 63(64)/2 = 2016

Or maybe you meant sum 0+7+14+ 21 + .... 63 ? IF so, factor out 7 to get

7(1+2+3+4+5+6+7+8+9)= 7(9)(10)/2 = 7(45) = 315