\(\frac{2.3+6.9+10.15+14.21}{2.5+6.15+10.25+14.35}\)

Rút gọn:

\(=\frac{3}{5}+\frac{3}{5}+\frac{3}{5}+\frac{3}{5}\)

\(=\frac{12}{5}\)

\(\frac{2.3+6.9+10.15+14.21}{2.5+6.15+10.25+14.35}=\frac{2.3+6.3.3+10.5.3+14.7.3}{2.5+6.3.5+10.5.5+14.7.5}\)

\(=\frac{3\left(2.1+6.3+10.5+14.7\right)}{5\left(2.1+6.3+10.5+14.7\right)}=\frac{3}{5}\)

\(\dfrac{2\cdot3-4\cdot6+6\cdot9}{2\cdot5-4\cdot10+6\cdot15}\)

\(=\dfrac{2\cdot3\left(1-2\cdot2+3\cdot3\right)}{2\cdot5\left(1-2\cdot2+3\cdot3\right)}\)

\(=\dfrac{3}{5}\)

99x101x103:6

6.B=1.3.6+3.5.6+5.7.6+...+95.97.6+97.99.6

6.B=1.3.(5+1)+3.5.(7-1)+5.7.(9-3)+...+95.97.(99-93)+97.99(101-95)

6.B=1.3.5+1.3+3.5.7-1.3.5+5.7.9-3.5.7+...+95.97.99-93.95.97+97.99.101-95.97.99=1.3+97.99.101

B=(3+97.99.101)/6

\(C=\frac{1}{1.3}+\frac{1}{3.5}+...+\frac{1}{35.37}\)

\(C=\frac{1}{2}.\left(\frac{2}{1.3}+\frac{2}{3.5}+...+\frac{2}{35.37}\right)\)

\(C=\frac{1}{2}.\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+...+\frac{1}{35}-\frac{1}{37}\right)\)

\(C=\frac{1}{2}.\left(1-\frac{1}{37}\right)\)

\(C=\frac{1}{2}.\frac{36}{37}\)

\(C=\frac{18}{37}\)

\(C=\frac{1}{1.3}+\frac{1}{3.5}+...+\frac{1}{35.37}\)

\(C=\frac{1}{2}\cdot\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+...+\frac{1}{35}-\frac{1}{37}\right)\)

\(C=\frac{1}{2}\cdot\left(1-\frac{1}{37}\right)\)

\(C=\frac{1}{2}\cdot\frac{36}{37}=\frac{18}{37}\)

Vay C = \(\frac{18}{37}\)

\(C=\frac{1}{1.3}+\frac{1}{3.5}+\frac{1}{5.7}+...+\frac{1}{35.37}\)

\(C=\frac{1}{2}.\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{35}-\frac{1}{37}\right)\)

\(C=\frac{1}{2}.\left(1-\frac{1}{37}\right)\)

\(C=\frac{1}{2}.\frac{36}{37}\)

\(C=\frac{18}{37}\)

\(\dfrac{4}{1.3}+\dfrac{4}{3.5}+\dfrac{4}{5.7}+...+\dfrac{4}{99.101}\)
\(=2\left(\dfrac{2}{1.3}+\dfrac{2}{3.5}+\dfrac{2}{5.7}+...+\dfrac{2}{99.101}\right)\)
\(=2\left(1-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+...+\dfrac{1}{99}-\dfrac{1}{101}\right)\)
\(=2\left(1-\dfrac{1}{101}\right)\)
\(=2\cdot\dfrac{100}{101}\)
\(=\dfrac{200}{101}\)

`c)4/1.3+4/3.5+4/5.7+...+4/99.101`

`=2(2/1.3+2/3.5+2/5.7+...+2/99.101)`

`=2(1/1-1/3+1/3-1/5+1/5-1/7+..+1/99-1/101)`

`=2(1/1-1/101)`

`=2(101/101-1/101)`

`=2 . 100/101`

`=200/101`

\(\dfrac{4}{1.3}+\dfrac{4}{3.5}+\dfrac{4}{5.7}+...+\dfrac{4}{99.101}\\ =\dfrac{4}{2}.\left(1-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+...+\dfrac{1}{99}-\dfrac{1}{101}\right)\\ =2.\left(1-\dfrac{1}{101}\right)\\ =2.\dfrac{100}{101}\\ =\dfrac{200}{101}\)

tA CÓ :

\(\frac{5.6+5.7}{5.8+20}=\frac{5\left(6+7\right)}{5.\left(8+4\right)}=\frac{5.13}{5.12}=\frac{13}{12}\)

\(\frac{8.9-4.15}{12.7-180}=\frac{3.4\left(2.3-5\right)}{12\left(7-15\right)}=\frac{12\left(6-5\right)}{12\left(7-15\right)}=\frac{6-5}{7-15}=\frac{1}{-8}\)

A=343200

Bạn zô đây nha: https://olm.vn/hoi-dap/question/839400.html

so so hang :   (99.102-1.4):1.1+1=89.82

gia tri cua A :    (99.102+1.4)x89.82:2= 4513.54482

mk đâu tien k cho mk nha

Ta suy ra:

4x-6x = 10-20

=> -2x = -10

=> x= -10/-2 = 5

Vay: x=5