Question

[Tiểu thư họ Vũ]

tìm x biết : x/2+x/6+x/12+x/20+...+x/132=11/2

Answer 1

[Nguyễn Thị Khánh Ly]

x/1*2+x/2*3+x/3*4+...+x/11*12=11/2 x-x/2+x/2-x/3+x/3-x/4+...+x/11-x/12=11/2 x-x/12=11/2 12x/12-x/12=66/12 11x/12=66/12 11x=66 x=6