Question

Jen

想問這三題🙏謝謝

1
1
(2)
+
+
+...+
1'1+2'1+2+3
480.1 10. (80 F
1+2+3++n
=
(3) 12-22 + 32-4² + + (2n-1)² - (2n)² + (2n+1)²=
(4)
1x(2n-1)+2x(2n-3)+3x(2n-5)+...+nx1=