Đặt \(A=1.2+2.3+...+98.99\)

\(3A=1.2.3+2.3.\left(4-1\right)+3.4.\left(5-2\right)+....+98.99.\left(100-97\right)\)

\(3A=1.2.3+2.3.4-1.2.3+...+98.99.100-97.98.99\)

\(3A=98.99.100\Rightarrow A=\frac{98.99.100}{3}\)

\(\Rightarrow\frac{\frac{98.99.100}{3}.x}{26950}=\frac{-60}{7}\)\(\Rightarrow98.99.100.x=-\frac{60}{7}.80850\)

\(\Rightarrow98.99.100.x=-693000\)

Đến đây bạn tự tính nhé

cảm ơn bạn nhé, nếu không có bạn chắc mai mình bị cô mắng chết

bạn nào nhanh mk tick cho nha

(1.2 + 2.3 + 3.4 +...+ 98.99) . \(\dfrac{x}{26950}\) = \(\dfrac{90}{7}\):1,5

Áp dụng ct: 1.2 + 2.3+ 3.4 +....+n.(n+1) = n(n+1)(n+2):3

Ta có:

\(\dfrac{98.99.100}{3}\).\(\dfrac{x}{26950}\)  =  \(\dfrac{90}{7}\):\(\dfrac{3}{2}\)

12\(x\) = \(\dfrac{60}{7}\)

     \(x\) = \(\dfrac{60}{7}\): 12

     \(x\) = \(\dfrac{5}{7}\) 

Khó quá mk chịu thôi bạn giải giùm mk nha

k mình đi

kb luôn nhé

kb nha

bai gi ma kho hieu qua ????

x=1 và x=\(\dfrac{4}{7}\)

bạn giải ra hộ mình mk tick cho nhé

Đặt (1.2+2.3+3.4+..+98.99)=a

=>3a= 1.2.(3-0)+2.3.(4-1).....98.99.(100-97)

=>3a=1.2.3-0+2.3.4-1.2.3+...+98.99.100-97.98.99

=>3a=98.99.100

=>a-98.99.100/3=323400

Thay vào,ta được

323400.x/26950=12

=>323400.x=12.26950=323400

=>x=1

6/7:1.5=4/7

\(\dfrac{\left(1.2+2.3+3.4+...+98.99\right).x}{26950}=12\dfrac{6}{7}:\dfrac{-3}{2}\\ \Rightarrow\left(1.2+2.3+3.4+...+98.99\right).x:26950=\dfrac{90}{7}:\dfrac{-3}{2}\\ \left(1.2+2.3+3.4+...+98.99\right).x:26950=\dfrac{-60}{7}\\ \left(1.2+2.3+3.4+...+98.99\right).x=\dfrac{-60}{7}.26950\\ \left(1.2+2.3+3.4+...+98.99\right).x=-231000\\ \left\{\left[99.98.\left(98+2\right)\right]:3\right\}.x=-231000\\ 323400x=-231000\\ x=-231000:323400\\ x=\dfrac{-5}{7}\)

Đặt A=1.2+2.3+...+98.99

=>3A=1.2.3+2.3.(4-1)+...+98.99.(100-97)

=1.2.3-1.2.3+2.3.4-...-97.98.99+98.99.100

=98.99.100

=>A=98.99.100:3=323400

=>\(\dfrac{323400x}{26950}=\dfrac{90}{7}\cdot\dfrac{2}{-3}\)

<=>12x=\(-\dfrac{60}{7}\)

<=>x=\(-\dfrac{60}{12.7}\)

<=>x=\(-\dfrac{5}{7}\)

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