=>(\(\frac{7}{4}+\frac{21}{20}+\frac{7}{10}+\frac{1}{2}\))-x=-2015

=>(1,75+1,05+0,7+0,5)-x=-2015

=>4-x=-2015

=>x=4-(-2015)

=>x=2019

(\(\frac{2121}{1212}+\frac{2121}{2020}+\frac{2121}{3030}+\frac{2121}{4242}\)) - x = -2015

=> ( \(\frac{21}{12}+\frac{21}{20}+\frac{21}{30}+\frac{21}{42}\) ) - x = -2015

=> ( \(\frac{7}{4}+\frac{21}{20}+\frac{21}{30}+\frac{1}{2}\) ) - x = -2015

=> ( 1,75 + 1,05 + 0,7 + 0,5 ) - x = -2015

=> 4 - x = -2015

=> x = 4 - ( -2015 )

=> x = 4 + 2015

=> x = 2019

Ai làm đúng và nhanh nhất mk k cho

cái thứ hai lớn hơn

Ta có : \(\frac{1212+1313+1414+1515+1616}{1717+1818+1919+2020+2121}=\frac{12+13+14+15+16}{17+18+19+20+21}=\frac{28\cdot\frac{5}{2}}{38\cdot\frac{5}{2}}=\frac{14}{19}\)

Dễ thấy \(\frac{111111}{666665}< \frac{1}{2}\) ( do 111111 < 666665/2 ) và \(\frac{14}{19}>\frac{1}{2}\) ( do 14 > 19/2 )

Vậy \(\frac{111111}{666665}< \frac{1212+1313+1414+1515+1616}{1717+1818+1919+2020+2121}\)

1212+2121+4242+2424

=1212+2121+2121+2121+1212+1212

=(1212+2121)+(2121+1212)+(1212+2121)

=3333+3333+3333

=3333 x 3 =9999

1212+2121+4242+2424=

=3333+6666

=9999

\(\frac{242}{363}+\frac{1616}{2121}=\frac{2}{7}.\frac{2015}{A}\)

\(\frac{11.11.2}{11.11.3}+\frac{101.16}{101.21}=\frac{2}{7}.\frac{2015}{A}\)

\(\frac{2}{3}+\frac{16}{21}=\frac{2}{7}.\frac{2015}{A}\)

\(\Rightarrow\frac{2}{7}.\frac{2015}{A}=\frac{10}{7}\)

\(\frac{2015}{A}=\frac{10}{7}:\frac{2}{7}\)

\(\frac{2015}{A}=5\)

\(A=2015:5\)

\(A=403\)

\(\left(\frac{242}{363}+\frac{1616}{2121}\right)=\frac{2}{7}.\frac{2015}{A}\)

\(\Leftrightarrow\left(\frac{2}{3}+\frac{16}{21}\right)=\frac{2}{7}.\frac{2015}{A}\)

\(\Leftrightarrow\frac{10}{7}=\frac{2}{7}.\frac{2015}{A}\)

\(\Leftrightarrow5=\frac{2015}{A}\)

\(\Leftrightarrow A=403\)

10/7 = 2/7 . 2015/A

2015/A = 10/7 / 2/7 = 5

2015/A = 5/1

A = 2015 / 5 = 403

\(\frac{1414+1515+1616+1717+1818+1919}{2020+2121+2222+2323+2424+2525}=\frac{9999}{13635}=\frac{11}{15}\)

\(A=\frac{7}{4}X\left(\frac{11}{4}+\frac{33}{20}+\frac{11}{10}+\frac{11}{14}\right)\)

\(A=\frac{7}{4}X\frac{44}{7}=11\)

18 x \(\left(\frac{1919}{2121}+\frac{888}{999}\right)\)

= 18 x \(\frac{113}{63}\)

= \(\frac{226}{7}\)

Đây có phải tính nhanh không bạn?

\(18\cdot\left(\frac{1919}{2121}+\frac{888}{999}\right)\)

Rút gọn:

\(\frac{1919}{2121}=\frac{1919:101}{2121:101}=\frac{19}{21}\)

\(\frac{888}{999}=\frac{888:111}{999:111}=\frac{8}{9}\)

Ta có:

\(18\cdot\left(\frac{19}{21}+\frac{8}{9}\right)\)

=\(18\cdot\left(\frac{57}{63}+\frac{56}{63}\right)\)

\(=18\cdot\frac{113}{63}\)

\(\frac{18.113}{63}=\frac{9\cdot2\cdot113}{9\cdot7}=\frac{2\cdot113}{7}=\frac{226}{7}\)

Kết quả là \(\frac{226}{7}\)

Đúng thì tk nha!!!

\(\frac{2323+1313+1414+1515+1616}{4141+2222+2323+2424+2525}\)

=\(\frac{8181}{13635}\)

18180,8               

\(\frac{1414+1515+1616+1717+1818+1919}{2020+2121+2222+2323+2424+2525}\)

\(=\frac{101\times\left(14+15+16+17+18+19\right)}{101\times\left(20+21+22+23+24+25\right)}\)

\(=\frac{14+15+16+17+18+19}{20+21+22+23+24+25}\)

+) Tử số :

Số các số hạng là : ( 19 - 14 ) : 1 + 1 = 6 ( số )

Tổng là : ( 19 + 14 ) x 6 : 2 = 99

+) Mẫu số :

Số các số hạng là : ( 25 - 20 ) : 1 + 1 = 6 ( số )

Tổng là : ( 25 + 20 ) x 6 : 2 = 135

\(\Leftrightarrow\frac{99}{135}=\frac{11}{15}\)