2x (x-1) =3(1-x)

2x²-2x=3-3x

2x²-2+3x=3

2x²-2x+3-3=0

2x²-2x+0=0

x₁=1 ; x₂=0

x2 sai roi

Mk nghĩ là chữ " tôi" 

người

EDOKAWA CONAN [ KUDO SHINICHI]

\(T=1\cdot2\cdot3+2\cdot3\cdot4+...+20\cdot21\cdot22\)

\(4T=1\cdot2\cdot3\cdot4+2\cdot3\cdot4\cdot4+...+20\cdot21\cdot22\cdot4\)

\(4T=1\cdot2\cdot3\cdot\left(4-0\right)+2\cdot3\cdot4\cdot\left(5-1\right)+..+20\cdot21\cdot22\cdot\left(23-19\right)\)

\(4T=0\cdot1\cdot2\cdot3-1\cdot2\cdot3\cdot4+2\cdot3\cdot4\cdot5-1\cdot2\cdot3\cdot4+..+20\cdot21\cdot22\cdot23-19\cdot20\cdot21\cdot22\)

\(4T=21\cdot22\cdot23\cdot24\)

\(T=\frac{21\cdot22\cdot23\cdot24}{4}=21\cdot22\cdot23\cdot6=63756\\ k.cho.mk.nha\)

1.2.3+2.3.4+3.4.5+...+20.21.22

=1/4.(1.2.3.4+2.3.4.4+3.4.5.4+...+20.21.22.4)

=1/4.[1.2.3.(4-0)+2.3.4.(5-1)+3.4.5.(6-2)+...+20.21.22.(23-19)]

=1/4.(1.2.3.4+2.3.4.5-1.2.3.4+3.4.5.6-2.3.4.5+....-19.20.21.22+20.21.22.23)

=1/4.20.21.22.23

=53130

\(B=\frac{1}{2^2}+\frac{1}{3^2}+\frac{1}{4^2}+...+\frac{1}{56^2}>\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+\frac{1}{4\cdot5}+...+\frac{1}{56\cdot57}\)

\(=\frac{1}{2}-\frac{1}{3}+...+\frac{1}{56}-\frac{1}{57}\)

\(=\frac{1}{2}-\frac{1}{57}=\frac{55}{114}< \frac{114}{114}=1\)

dung phân bò để nuôi giun là vì

+đất thị nhẹ, phân bò có nhiều chất dinh dưỡng

+đất thì nhẹ, phân bò giúp giun dễ sống hơn

Ta có: 

\(\frac{A}{5}=\frac{4}{35\cdot31}+\frac{6}{35\cdot41}+\frac{9}{50\cdot41}+\frac{7}{50\cdot57}=\frac{35-31}{35\cdot31}+\frac{41-35}{35\cdot41}+\frac{50-41}{50\cdot41}+\frac{57-50}{50\cdot57}\)    ( Ps cuối là\(\frac{57-50}{50.57}\) nha).

\(=\frac{1}{31}-\frac{1}{35}+\frac{1}{35}-\frac{1}{41}+\frac{1}{41}-\frac{1}{50}+\frac{1}{50}-\frac{1}{57}\) 

\(\Rightarrow\frac{A}{5}=5\cdot\left(\frac{1}{31}-\frac{1}{57}\right)\) 

Tương tự:

\(\frac{B}{2}=\frac{7}{38.31}+\frac{5}{38.43}+\frac{3}{43.46}+\frac{11}{46.57}=\frac{38-31}{38.31}+\frac{41-38}{38.41}+\frac{46-43}{43.46}+\frac{57-46}{46.57}\) 

\(=\frac{1}{31}-\frac{1}{38}+\frac{1}{38}-\frac{1}{43}+\frac{1}{43}-\frac{1}{46}+\frac{1}{46}-\frac{1}{57}\) 

\(\Rightarrow\frac{B}{2}=2\cdot\left(\frac{1}{31}-\frac{1}{57}\right)\) 

Từ đó, suy ra:

\(\frac{A}{B}=\frac{5}{2}\) 

Vậy \(\frac{A}{B}=\frac{5}{2}\)

P/s: Có gì thừa hay thiếu thì bạn thêm hoặc bớt đi nha.

~Hk tốt~

con chó

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