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Ta có:
Đặt A=1.2.3+2.3.4+3.4.5+....+99.100.101
4A=1.2.3.(4-0)+2.3.4.(5-1)+3.4.5.(6-2)+.....+99.100.101(102-98)
4A=1.2.3.4-0.1.2.3+2.3.4.5-1.2.3.4+3.4.5.6-2.3.4.5+.......+99.100.101.102-98.99.100.101
4A=99.100.101.102
=> A=\(\frac{99.100.101.102}{4}=25497450\)
Bạn tự đáp số nhé...
\(\frac{3.4.5}{10.2.6}=\frac{3.4.5}{2.5.2.2.3}=\frac{3.4.5}{2.5.4.3}=\frac{1}{2}\)
1.
a) \(\frac{16}{24}-\frac{1}{3}=\frac{16}{24}-\frac{8}{24}=\)\(\frac{8}{24}=\frac{1}{3}\)
b) \(\frac{4}{5}-\frac{12}{60}=\frac{48}{60}-\frac{12}{60}=\frac{36}{60}=\frac{9}{15}\)
3.
a)\(\frac{17}{6}-\frac{2}{6}=\frac{17-2}{6}=\frac{15}{6}\)
b) \(\frac{16}{15}-\frac{11}{15}=\frac{16-11}{15}=\frac{5}{15}=\frac{1}{3}\)
c) \(\frac{19}{12}-\frac{13}{12}=\frac{19-13}{12}=\frac{6}{12}=\frac{1}{2}\)
a) 16 24 − 1 3 = 16 24 − 8 24 = 24 16 − 3 1 = 24 16 − 24 8 = 8 24 = 1 3 24 8 = 3 1 b) 4 5 − 12 60 = 48 60 − 12 60 = 36 60 = 9 15 5 4 − 60 12 = 60 48 − 60 12 = 60 36 = 15 9 3. a) 17 6 − 2 6 = 17 − 2 6 = 15 6 6 17 − 6 2 = 6 17−2 = 6 15 b) 16 15 − 11 15 = 16 − 11 15 = 5 15 = 1 3 15 16 − 15 11 = 15 16−11 = 15 5 = 3 1 c) 19 12 − 13 12 = 19 − 13 12 = 6 12 = 1 2 12 19 − 12 13 = 12 19−13 = 12 6 = 2 1
\(\frac{2}{3}+\frac{3}{9}+\frac{7}{5}\)
\(=\frac{2}{3}+\frac{1}{3}+\frac{7}{5}\)
\(=\frac{10}{15}+\frac{5}{15}+\frac{21}{15}\)
\(=\frac{36}{15}\)
\(=\frac{12}{5}\)
\(\frac{2}{3}+\frac{3}{9}+\frac{7}{5}\)
=\(\frac{2}{3}+\frac{1}{3}+\frac{7}{5}\)
=\(\frac{7}{5}+\frac{2}{3}+\frac{1}{3}\)
=\(\frac{3}{3}+\frac{7}{5}\)
\(=1+\frac{7}{5}\)
=\(\frac{12}{5}\)
\(\frac{8}{5}-\frac{18}{27}\)
\(=\frac{8}{5}-\frac{2}{3}\)
\(=\frac{24}{15}-\frac{10}{15}\)
\(=\frac{14}{15}\)
\(\frac{12}{20}-\frac{6}{18}\)
\(=\frac{3}{5}-\frac{1}{3}\)
\(=\frac{9}{15}-\frac{5}{15}\)
\(=\frac{4}{15}\)
\(\frac{8}{24}-\frac{5}{25}\)
\(=\frac{1}{3}-\frac{1}{5}\)
\(=\frac{5}{15}-\frac{3}{15}\)
\(=\frac{2}{15}\)
\(\frac{18}{21}-\frac{12}{27}\)
\(=\frac{6}{7}-\frac{4}{9}\)
\(=\frac{54}{63}-\frac{28}{63}\)
\(=\frac{26}{63}\)
1)8/5-2/3=14/15
2)3/5-1/3=4/15
3)1/3-1/5=2/15
4)6/7-4/9=26/63
\(=\frac{3}{4}\left(\frac{8}{9}+\frac{2}{3}\right)=\frac{3}{4}\left(\frac{8}{9}+\frac{6}{9}\right)=\frac{3}{4}x\frac{14}{9}=\frac{7}{6}..\)
mình nhầm chỗ \(\frac{8}{9}\)và \(\frac{3}{4}\)có một dấu cộng
A = 1.2.3+2.3.4+...+99.100.101
⇒ 4A = 1.2.3.4+2.3.4.(5−1)+...+99.100.101.(102−98)
=1.2.3.4+2.3.4.5−1.2.3.4+...+99.100.101.102−98.99.100.101
=99.100.101.102=99.100.101.102
⇒A = 99.100.101.102 : 4 = 90.25.101.102
Vậy...
Mà đây là câu hỏi lớp lớn sao bạn đăng lên toán lớp 4 vậy ??
Đặt \(S=1.2.3+2.3.4+3.4.5+...+99.100.101\)
\(\Rightarrow4S=1.2.3.4+2.3.4.4+3.4.5.4+...+99.100.101.4\)
\(4S=1.2.3.4+2.3.4.\left(5-1\right)+3.4.5\left(6-2\right)+...+99.100.101\left(102-98\right)\)
\(4S=1.2.3.4+2.3.4.5-1.2.3.4+3.4.5.6-2.3.4.5+...+99.100.101.102-98.99.100.101\)
\(4S=99.100.101.102\)\(\Rightarrow S=\frac{99.100.101.102}{4}=25497450\)