Question

Tìm x biết (2+x)+(4+x)+(6+x)+...+(52+x)=780

Answer 1

(2+x)+(4+x)+...+(52+x)=780

(2+4+...+52)+(x+...+x)=780

26x+702=780

26x=780-702

26x=78

x=78/26

x=3

Answer 2

(2 + x) + (4 + x) + ...... + (52  + x) = 780

702 + 26x = 780

26x = 78

=> x = 3