\(a,\dfrac{5}{4}+\dfrac{7}{3}=\dfrac{15}{12}+\dfrac{28}{12}=\dfrac{43}{12}\\ b,\dfrac{4}{5}\times\dfrac{5}{8}=\dfrac{4}{8}=\dfrac{1}{2}\\ c,\dfrac{2}{3}-\dfrac{3}{8}=\dfrac{16}{24}-\dfrac{9}{24}=\dfrac{7}{24}\\ d,\dfrac{5}{6}:\dfrac{1}{3}=\dfrac{5}{6}\times\dfrac{1}{3}=\dfrac{5}{18}\)

a) \(\dfrac{5}{4}+\dfrac{7}{3}=\dfrac{15}{12}+\dfrac{28}{12}=\dfrac{43}{12}\)

b) \(\dfrac{4}{5}\cdot\dfrac{5}{8}=\dfrac{20}{40}=\dfrac{1}{2}\)

c) \(\dfrac{2}{3}-\dfrac{3}{8}=\dfrac{16}{24}-\dfrac{9}{24}=\dfrac{7}{24}\)

d) \(\dfrac{5}{6}:\dfrac{1}{3}=\dfrac{5}{6}\cdot\dfrac{3}{1}=\dfrac{15}{6}\)

\(\frac{3}{9}\cdot\frac{5}{4}=\frac{1}{3}\cdot\frac{5}{4}\)

\(=\frac{1.5}{3.4}\)

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

3/9=1/3

5/4=5/4(ko rút gọn đc)

3/9x5/4=5/12

NHỚ K CHO MK NHA

15/16

a) \(15\sqrt{\dfrac{4}{3}}-5\sqrt{48}+2\sqrt{12}-6\sqrt{\dfrac{1}{3}}\)

\(=\sqrt{15^2\cdot\dfrac{4}{3}}-5\cdot4\sqrt{3}+2\cdot2\sqrt{3}-\sqrt{6^2\cdot\dfrac{1}{3}}\)

\(=\sqrt{\dfrac{225\cdot4}{3}}-20\sqrt{3}+4\sqrt{3}-\sqrt{\dfrac{36}{3}}\)

\(=\sqrt{75\cdot4}-16\sqrt{3}-\sqrt{12}\)

\(=10\sqrt{3}-16\sqrt{3}-2\sqrt{3}\)

\(=-8\sqrt{3}\)

b) \(\dfrac{15}{\sqrt{6}+1}-\dfrac{3}{\sqrt{7}-\sqrt{2}}-15\sqrt{6}+3\sqrt{7}\)

\(=\dfrac{15\left(\sqrt{6}-1\right)}{\left(\sqrt{6}+1\right)\left(\sqrt{6}-1\right)}-\dfrac{3\left(\sqrt{7}+\sqrt{2}\right)}{\left(\sqrt{7}-\sqrt{2}\right)\left(\sqrt{7}+\sqrt{2}\right)}-15\sqrt{6}+3\sqrt{7}\)

\(=\dfrac{15\left(\sqrt{6}-1\right)}{6-1}-\dfrac{3\sqrt{7}+3\sqrt{2}}{7-2}-15\sqrt{6}+3\sqrt{7}\)

\(=3\left(\sqrt{6}-1\right)-\dfrac{3\sqrt{7}+3\sqrt{2}}{5}-15\sqrt{6}+3\sqrt{7}\)

\(=3\sqrt{6}-3-\dfrac{3\sqrt{7}+3\sqrt{2}}{5}-15\sqrt{6}+3\sqrt{7}\)

\(=-12\sqrt{6}-3+3\sqrt{7}-\dfrac{3\sqrt{7}+3\sqrt{2}}{5}\)

\(=\dfrac{-60\sqrt{6}-15+15\sqrt{7}-3\sqrt{7}-3\sqrt{2}}{5}\)

\(=\dfrac{-60\sqrt{6}-15+12\sqrt{7}-3\sqrt{2}}{5}\)

`a) 5 / 13 xx 4 / 15 xx 13 = [ 5 xx 4 xx 13 ] / [ 13 xx 5 xx 3 ] = 4 / 3`

`b) ( 3 / 7 + 5 / 2 ) xx 7 / 5 = 3 / 7 xx 7 / 5 + 5 / 2 xx 7 / 5 = 3 / 5 + 7 / 2 = 6 / 10 + 35 / 10 = 41 / 10`

`c) 1 / 5 xx 11 / 18 + 11 / 18 xx 3 / 5 = 11 / 18 xx ( 1 / 5 + 3 / 5 ) = 11 / 18 xx 4 / 5 = [ 11 xx 2 xx 2 ] / [ 2 xx 9 xx 5 ] = 22 / 45`

\(a,\dfrac{5}{13}\times\dfrac{4}{15}\times13=\dfrac{4}{3}\)

\(b,\left(\dfrac{3}{7}+\dfrac{5}{2}\right)\times\dfrac{7}{5}=\left(\dfrac{6}{14}+\dfrac{35}{14}\right)\times\dfrac{7}{5}=\dfrac{41}{14}\times\dfrac{7}{15}=\dfrac{41}{30}\)

\(c,\dfrac{1}{5}\times\dfrac{11}{18}+\dfrac{11}{18}\times\dfrac{3}{5}=\dfrac{11}{18}\times\left(\dfrac{1}{5}+\dfrac{3}{5}\right)=\dfrac{11}{18}\times\dfrac{4}{5}=\dfrac{22}{45}\)

3/2 x 4/9 x 2/4

= 24/72

= 1/3

`3/2xx4/9xx2/4=[3xx4xx2]/[2xx3xx3xx4]=1/3`

3/2x4/9x2/4

=2/3x2/4

=4/12

=1/3

a: =35/17-18/17-9/5+4/5

=1-1=0

b: =-7/19(3/17+8/11-1)

=7/19*18/187=126/3553

c: =26/15-11/15-17/3-6/13

=1-6/13-17/3

=7/13-17/3=-200/39

Gợi ý: Nó trong VBT Toán Nâng Cao

bó tay !

a, S= 1.2 + 2.3 + 3.4 + 4.5 + 99.100

   -S= 1/1 - 1/2 + ......... + 1/4 -1/5 + [-(99.100)]

      = 1/1 - 1/5 + [-(99.100)]

      = 4/5 - 99/100

      =-19/100

S  = 19/100

Vậy S = 19/100

k mk nha

a) \(S=1.2+2.3+...+99.100\)

\(\Rightarrow3S=1.2.3+2.3.3+...+99.100.3\)

\(=1.2.3+2.3.\left(4-1\right)+...+99.100.\left(101-98\right)\)

\(=1.2.3+2.3.4-1.2.3+...+99.100.101-98.99.100\)

\(=99.100.101\)

\(=999900\)

\(\Rightarrow S=\frac{999900}{3}=333300\)

ai nhNH MK K