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7,2 x 13 + 3,6 x 71 + 3,6 + 7,2
= 3,6 x 2 x 13 + 3,6 x 71 + 1,2 x 3 + 7,2
= 3,6 x 26 x 71 + 1,2 x 3 + 7,2
= 3,6 x (26 + 71 + 3)
= 3,6 x 100
= 360
1,2 x 15 + 0,4 x 7 + 1,2 x 16
= 0,4 x 3 x 15 + 04 x 7 + 0,4 x 3 x 16
= 0,4 x 45 + 0,4 x 7 + 0,4 x 48
= 0,4 x (45 + 7 + 48)
= 0,4 x 100
= 40
\(\text{7,2 x 13 + 3,6 x 71 + 3,6 + 7,2 = 3,6 x 2 x 13 + 3,6 x 71 + 1,2 x 3 + 7,2 }\)
\(\text{= 3,6 x 26 x 71 + 1,2 x 3 + 7,2 = 3,6 x (26 + 71 + 3) }\)\(\text{= 3,6 x 100 = 360}\)
\(\text{1,2 x 15 + 0,4 x 7 + 1,2 x 16 = 0,4 x 3 x 15 + 04 x 7 + 0,4 x 3 x 16}\)
\(\text{= 0,4 x 45 + 0,4 x 7 + 0,4 x 48 = 0,4 x (45 + 7 + 48)}\)
\(\text{= 0,4 x 100 = 40}\)
a)
= 35,16 + 44,84 : 4 - 15,6
= 35,16 + 11,21 - 15,6
= 30,77
b)
= 45,65 x 73 + 22 x 45,65 + 45,65 x 5
= 45,65 x (73 + 22 + 5)
= 45,65 x 100
= 4565
- 1,8+0,66+1,2+0,34
=(1,8+1,2)+(0,66+0,34)=3+1=4
- 6,48 x 1125 - 6,48 x 112 - 6,48 x 13
=6,48 x (1125-112 -13)=6,48 x 1000= 6480
- 24,5 x 4,8 + 15,6 x 4,8
=4,8 x ( 24,5 +15,6)=4,8 x 40,1 =192,48
Giải:
\(\dfrac{1}{3.5}+\dfrac{1}{5.7}+\dfrac{1}{7.9}+...+\dfrac{1}{x.\left(x+2\right)}=\dfrac{16}{99}\)
\(\dfrac{1}{2}.\left(\dfrac{2}{3.5}+\dfrac{2}{5.7}+\dfrac{2}{7.9}+...+\dfrac{2}{x.\left(x+2\right)}\right)=\dfrac{16}{99}\)
\(\dfrac{1}{2}.\left(\dfrac{1}{2}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{9}+...+\dfrac{1}{x}-\dfrac{1}{x+2}\right)=\dfrac{16}{99}\)
\(\dfrac{1}{2}.\left(\dfrac{1}{3}-\dfrac{1}{x+2}\right)=\dfrac{16}{99}\)
\(\dfrac{1}{3}-\dfrac{1}{x+2}=\dfrac{16}{99}:\dfrac{1}{2}\)
\(\dfrac{1}{3}-\dfrac{1}{x+2}=\dfrac{32}{99}\)
\(\dfrac{1}{x+2}=\dfrac{1}{3}-\dfrac{32}{99}\)
\(\dfrac{1}{x+2}=\dfrac{1}{99}\)
\(\Rightarrow x+2=99\)
\(x=99-2\)
\(x=97\)
Chúc em học tốt!
\(\dfrac{1}{3x5}+\dfrac{1}{5x7}+\dfrac{1}{7x9}+...+\dfrac{1}{x\left(x+2\right)}=\dfrac{16}{99}\)
\(=\dfrac{1}{2}\left(\dfrac{2}{3x5}+\dfrac{2}{5x7}+...+\dfrac{2}{x\left(x+2\right)}\right)=\dfrac{16}{99}\)
\(=\dfrac{2}{3x5}\)\(+\dfrac{2}{5x7}+...+\dfrac{2}{x\left(x+2\right)}=\dfrac{32}{99}\)
\(=\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+\dfrac{1}{7}+.....+\dfrac{1}{x}-\dfrac{1}{x+2}=\dfrac{32}{99}\)
\(=\dfrac{1}{3}-\dfrac{1}{x+2}=\dfrac{32}{99}=>x=97\)
\(\dfrac{x}{12}=x+\dfrac{15}{16}\)
\(\Leftrightarrow\dfrac{x}{12}=\dfrac{16x+15}{16}\)
\(\Rightarrow12\left(16x+15\right)=16x\)
\(\Leftrightarrow192x+180=16x\)
\(\Leftrightarrow176x=-180\)
\(\Leftrightarrow x=-\dfrac{45}{44}\)
Vậy \(x=-\dfrac{45}{44}\)
\(\dfrac{x}{12}=\dfrac{x+15}{16}\)
\(\Rightarrow12\left(x+15\right)=16x\)
\(\Leftrightarrow12x+180=16x\)
\(\Leftrightarrow4x=180\)
\(\Leftrightarrow x=45\)
Vậy x = 45
\(a,30+X=120:5+27\\ 30+X=24+27\\ 30+X=51\\ X=51-30=21\\ ---\\ b,40-3\times X=13\\ 3\times X=40-13=27\\ X=\dfrac{27}{3}=9\\ ---\\ 2\times X-8=16\\ 2\times X=16+8\\ 2\times X=24\\ X=\dfrac{24}{2}=12\\ \\---\\ \dfrac{1}{2}\times X-\dfrac{1}{3}=\dfrac{1}{4}\\ \dfrac{1}{2}\times X=\dfrac{1}{4}+\dfrac{1}{3}=\dfrac{7}{12}\\ X=\dfrac{7}{12}:\dfrac{1}{2}=\dfrac{7}{6}\)
k x 1,2 + k x 8,4 + k + k x 0,6 = 28
k x (1,2 + 8,4 + 1 + 0,6) = 28
k x 11,2 = 28
k = 28 : 11,2
k = 2,5
Vậy k = 2,5
k = k x ( 1,2 + 8,4 + 0,6) = 28
k = 28 : 10,2
k = 2,745098
Tích nha
k*1,2+k*8,4+k+k*0,6=28
=k*(1,2+8,4+1+0,6)=28
=k*11,2=28
\(\Rightarrow\)k=28:11,2
k=2,5