good luck ! :)

1500N nha!

-1

\(\dfrac{1}{a+1}+\dfrac{1}{a\left(a+1\right)}=\dfrac{a\left(a+1\right)}{\left(a+1\right)a\left(a+1\right)}+\dfrac{a+1}{a\left(a+1\right)\left(a+1\right)}\\ =\dfrac{a+1+a\left(a+1\right)}{a\left(a+1\right)\left(a+1\right)}=\dfrac{\left(a+1\right)\left(a+1\right)}{a\left(a+1\right)\left(a+1\right)}\\ =\dfrac{1}{a}\)

Suy ra \(\dfrac{1}{a}=\dfrac{1}{a+1}+\dfrac{1}{a\left(a+1\right)}\)

11000;10100;10010;10001;20000.

**** minh nha ^ ^

minh lam cau b

\(\dfrac{-1}{2}\cdot\dfrac{-2}{3}\cdot\cdot\cdot\cdot\cdot\dfrac{-999}{1000}\)

vi tu 1-999 co so cac so la le nen gia tri la so am

Neu tu la duong thi ta co :

\(\dfrac{1}{2}\cdot\dfrac{2}{3}\cdot\cdot\cdot\cdot\cdot\dfrac{999}{1000}\\ =\dfrac{1}{1000}\)

Nhung tu so phai la am \(\Rightarrow\)\(\dfrac{1}{1000}\) se phai la\(\dfrac{-1}{1000}\)

Vay dap an la \(\dfrac{-1}{1000}\)

x=-1

abbc=100.ab+bc

ab.ac.7-100.ab=bc

ab.(ac.7-100)=bc

\(\Rightarrow\) ac.7-100 < 10

\(\Rightarrow\) ac<16

\(\Rightarrow\) a=1

Ma ac.7-100=1c.7-100=c.7+70-100=c.7-30<10

\(\Rightarrow\) c.7<40

\(\Rightarrow\) c<6

va c.7-30>0

\(\Rightarrow\) c.7 >30

\(\Rightarrow\) c>4

\(\Rightarrow\) c=5

Ma 1c.7-100=15.7-100=5

\(\Rightarrow\) ab.5=bc

Hay 1b.5=b5

\(\Rightarrow\) 50+5b=10.b+5

\(\Rightarrow\) 5.b=45

\(\Rightarrow\) b=9

Vay a=1;b=9;c=5

Nhiệt kế là thiết bi dùng để đo nhiệt độ

24 tháng hay còn gọi là 2 năm bạn nhé :)