bạn viết mik ko hiểu cái j hết

. là dấu nhân hay dấu phẩy vậy bạn

b)[1,1*(-4,3+4,5)]:(-10+10,01)

(1,1*0,2):0,01

=0,22:0,01

=22

c)=(6,7+5,66-3,7+4,34)*(-76,6*1,2+7,66*10*1,2)

=(6,7+5,66-3,7+4,34)*(-76,6*1,2+76,6*1.2)

=(6,7+5,66-3,7+4,34)*[1,2*(-76,6+76,6)]

=(6,7+5,66-3,7+4,34)*(1,2*0)

=(6,7+5,66-3,7+4,34)*0

=0

\(a.\)

\(6,5+1,2+3,5-5,2+6,5-4,8\)

\(=\left(-5,2+1,2\right)+\left(3,5+6,5\right)+\left(6,5-4,8\right)\)

\(=\left(-4\right)+10+1,7\)

\(=6+1,7\)

\(=7,7\)

\(b.\)

\(\left(-4,3.1,1+1,1.4,5\right):\left(-0,5:0,05+10,01\right)\)

\(=\left[1,1.\left(-4,3+4,5\right)\right]:\left(-10+10.01\right)\)

\(=\left[1,1.0,2\right]:\left(0,01\right)\)

\(=0,22:0,01\)

\(=22\)

\(c.\)

\(\left(6,7+5,66-3,7+4,34\right).\left(-76,6.1,2+7,66.12\right)\)

\(=\left(6,7+5,66-3,7+4,34\right).\left[76,6\left(-1,2\right)+7,66.12\right]\)

\(=13.0\)

\(=0\)

\(=3\)

Số só hạng là : (14,9- 0,2):0,3+1=50

Tổng là: 50: 2 x (0,2+ 14.9)=27,98

bạn ghi rõ lại đề bài đi

Bài làm:

Ta có: \(F=\left(\frac{1.1}{1.2}\right).\left(\frac{2.2}{2.3}\right).\left(\frac{3.3}{3.4}\right)\left(\frac{4.4}{4.5}\right)\)

\(F=\frac{1}{2}.\frac{2}{3}.\frac{3}{4}.\frac{4}{5}\)

\(F=\frac{1}{5}\)

Bài làm 

\(F=\left(\frac{1.1}{1.2}\right)\left(\frac{2.2}{2.3}\right)\left(\frac{3.3}{3.4}\right)\left(\frac{4.4}{4.5}\right)\)

\(=\frac{1}{2}.\frac{2}{3}.\frac{3}{4}.\frac{4}{5}=\frac{1.2.3.4}{2.3.4.5}=\frac{1}{5}\)

Ảnh hiển thị bị lỗi hết rồi bạn. Bạn coi lại.

\(\dfrac{1}{1.2}+\dfrac{1}{2.3}+\dfrac{1}{3.4}+\dfrac{1}{4.5}+...+\dfrac{1}{x.\left(x+1\right)}=\dfrac{499}{500}\)

\(\Leftrightarrow1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+...+\dfrac{1}{x}-\dfrac{1}{x+1}=\dfrac{499}{500}\)

\(\Leftrightarrow1-\dfrac{1}{x+1}=\dfrac{499}{500}\)

\(\Leftrightarrow x=499\)

giúp e vs