cái này lớp 6 chưa học mà lớp 5 học là siêu đó

lớp mk lớp chọn mà

15

\(=15x\left(\dfrac{21}{43}+\dfrac{22}{43}\right)=15x1=15\)

\(a,=15\left(\dfrac{2121}{4343}+\dfrac{222222}{434343}\right)=15\left(\dfrac{21}{43}+\dfrac{22}{43}\right)=15\cdot1=15\)

Giai nhanh giup mik với ạ mik cần gấp.Làm hết ạ

\(1,\\ a,=\dfrac{7}{19}\times\left(\dfrac{1}{3}+\dfrac{2}{3}\right)=\dfrac{7}{19}\times1=\dfrac{7}{19}\\ b,=\dfrac{2}{5}+\left(\dfrac{3}{4}+\dfrac{1}{4}\right)=\dfrac{2}{5}+1=\dfrac{7}{5}\\ 2,\\ a,=15\times\left(\dfrac{2121}{4343}+\dfrac{222222}{434343}\right)\\ =15\times\left(\dfrac{2121:101}{4343:101}+\dfrac{222222:10101}{434343:10101}\right)\\ =15\times\left(\dfrac{21}{43}+\dfrac{22}{43}\right)=15\times\dfrac{43}{43}=15\times1=15\)

\(3,\)

Cạnh \(AC=\) chu vi ABC \(-AB-BC=\dfrac{4}{5}-\dfrac{1}{5}-\dfrac{1}{4}=\dfrac{3}{5}-\dfrac{1}{4}=\dfrac{7}{20}\left(m\right)\) 

Vì \(\dfrac{7}{20}>\dfrac{5}{20}>\dfrac{4}{20}\Rightarrow\dfrac{7}{20}>\dfrac{1}{4}>\dfrac{1}{5}\) nên \(AC>BC>AB\)

Bài 1 

a; \(\dfrac{7}{19}\) x \(\dfrac{1}{3}\) + \(\dfrac{7}{19}\) x \(\dfrac{2}{3}\)

= \(\dfrac{7}{19}\) x (\(\dfrac{1}{3}+\dfrac{2}{3}\))

= \(\dfrac{7}{19}\) x 1

= \(\dfrac{7}{19}\)

b; 15 x \(\dfrac{2121}{4343}\) + 15 x \(\dfrac{212121}{434343}\)

= 15 x \(\dfrac{21}{43}\) + 15 x \(\dfrac{21}{43}\)

= 15 x \(\dfrac{21}{43}\) x (1 + 1)

= 15 x \(\dfrac{21}{43}\) x 2

= (15 x 2) x \(\dfrac{21}{43}\)

= 30 x \(\dfrac{21}{43}\)

= \(\dfrac{630}{43}\)

1/2x3+1/3x4+1/4x5+1/5x6

= 1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6

=1/2-1/6

=1/3

15:x= 0.85+0.35

15:x= 1,2

    x= 15:1,2

     x= 12,5

nha bn, mk nghĩ vậy

Thank nhug dung ko

\(2022\times2005-2000\times2022+15\times2022-20\times2021\)

\(=2022\times\left(2005-2000+15\right)-20\times2021\)

\(=2022\times20-20\times2021\)

\(=20\times\left(2022-2021\right)\)

\(=20\times1\)

\(=20\)

a, 2022 \(\times\) 2005 - 2000 \(\times\) 2022 + 15 \(\times\) 2022 - 20 \(\times\) 2021

= (2022  \(\times\) 2005 - 2000 \(\times\) 2022 + 15 \(\times\) 2022 )- 20 \(\times\) 2021

= 2022 \(\times\) (2005 - 2000 + 15) - 20  \(\times\) 2021

= 2022 \(\times\) (5 +15)  - 20 \(\times\) 2021

= 2022 \(\times\) 20 - 20 \(\times\) 2021

= 20 \(\times\) (2022 - 2021)

= 20 \(\times\) 1

= 20 

câu b )

ta phân phối 2 vô 

=> \(\frac{2}{11.13}+\frac{2}{13.15}+\frac{2}{15.17}+\frac{2}{17.19}+\frac{x}{209}=\frac{10}{209}\)

\(\Rightarrow\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-\frac{1}{15}+...+\frac{1}{17}-\frac{1}{19}+\frac{x}{209}=\frac{10}{209}\)

\(\Rightarrow\frac{8}{209}+\frac{x}{209}=\frac{10}{209}\)

\(\Rightarrow\frac{x}{209}=\frac{2}{209}\)

\(\Rightarrow x=2\)

240 - (120 : x -15) x 20 = 140

        (120: x - 15)  x 20   =240-140

                (120: x - 15 ) = 100:20

                 (120:x-15)=5 

                   120:x=5+15

                    120:x=20

                     x=120:20=6