Toán Lớp 7: (1/1.3+1/3.5+1/5.7+…+1/13.15).(x-2)=1/15x-3

Question

Toán Lớp 7:  (1/1.3+1/3.5+1/5.7+…+1/13.15).(x-2)=1/15x-3

lanhuongthu · Answer

Lời giải và giải thích chi tiết:     (1/(1 . 3) + 1/(3 . 5) + ......... + 1/(13 . 15))(x - 2) = 1/15x - 3   &rarr; 1/2(2/(1 . 3) + 2/(3 . 5) + ......... + 2/(13 . 15))(x - 2) = 1/15x - 3   &rarr; 1/2(1 - 1/3 + 1/3 - 1/5 + .......... + 1/13 - 1/15)(x - 2) = 1/15x - 3   &rarr; 1/2(1 - 1/15)(x - 2) = 1/15x - 3   &rarr; 1/2 . 14/15(x - 2) = 1/15x - 3   &rarr; 7/15(x - 2) = 1/15x - 3   &rarr; 7/15x - 14/15 = 1/15x - 3   &rarr; 7/15x - 1/15x = -3 + 14/15   &rarr; 2/5x = (-31)/15   &rarr; x = (-31)/6   Vậy  x = (-31)/6

tuenhioanh · Answer

(1/(1.3)+1/(3.5)+...+1/(13.15))(x-2)=1/15x-3   1/2(2/(1.3)+2/(3.5)+...+2/(13.15))(x-2)=1/15x-3   1/2(1/1-1/3+1/3-1/5+1/5-1/7+...+1/13-1/15)(x-2)=1/15x-3   1/2(1/1-1/15)(x-2)=1/15x-3   1/2 . 14/15(x-2)=1/15-3   7/15(x-2)=1/15-3   7/15x-14/15=1/15-3   7/15x-1/15x=-3+14/15   2/5x=-31/15   x=-31/15:2/5   x=-31/6