gấp ạ

\(\dfrac{4}{15}=\dfrac{4\cdot24}{15\cdot24}=\dfrac{96}{360}\)

\(\dfrac{5}{72}=\dfrac{5\cdot5}{72\cdot5}=\dfrac{25}{360}\)

a có song song vs b.còn vì sao thì tui hog bt.

Nếu \(c\) vuông góc với đường thẳng \(a\) và \(b\) thì 2 góc so le sẽ bằng nhau (\(=90^o\)).

Vậy \(a//b\)

Bài 1:

Tổng của 2 số là

  \(36\times2=72\) 

Số lớn là

  \(72-17=55\) 

Bài 2:

a) \(4567+y\div34=10987\) 

                 \(y\div34=10987-4567\) 

                 \(y\div34=6420\) 

                         \(y=6420\times34\) 

                         \(y=218280\) 

b) \(\dfrac{4}{3}+\dfrac{1}{2}\div y=2\) 

             \(\dfrac{1}{2}\div y=2-\dfrac{4}{3}\) 

              \(\dfrac{1}{2}\div y=\dfrac{2}{3}\) 

                      \(y=\dfrac{1}{2}\div\dfrac{2}{3}\) 

                      \(y=\dfrac{3}{4}\) 

Bài 3:

a) \(\dfrac{2}{5}\times\dfrac{2}{5}+\dfrac{9}{8}\div3=\dfrac{4}{25}+\dfrac{9}{8}\times\dfrac{1}{3}=\dfrac{4}{25}+\dfrac{3}{8}=\dfrac{107}{200}\) 

b) \(2-\left(\dfrac{1}{7}\times4+\dfrac{5}{21}\right)=2-\left(\dfrac{4}{7}+\dfrac{5}{21}\right)=2-\dfrac{17}{21}=\dfrac{25}{21}\)

Bài 1 : Gọi a là số lớn, b là số bé, theo đề bài ta có :

(a+b):2=36⇒a+b=72

mà b=17

Nên a=72-17=55

Bài 2 :

a) 4567+y:34=10987

⇒ y:34=10987-4567

⇒ y:34=6420

⇒ y=6420x34

⇒ y=218280

b) \(\dfrac{4}{3}+\dfrac{1}{2}:y=2\)

\(\Rightarrow\dfrac{1}{2}:y=2-\dfrac{4}{3}\)

\(\Rightarrow\dfrac{1}{2}:y=\dfrac{2}{3}\)

\(\Rightarrow y=\dfrac{1}{2}:\dfrac{2}{3}\)

\(\Rightarrow y=\dfrac{1}{2}x\dfrac{3}{2}\)

\(\Rightarrow y=\dfrac{3}{4}\)

Bài 3 :

\(\dfrac{2}{5}x\dfrac{2}{5}+\dfrac{9}{8}:3=\dfrac{4}{25}+\dfrac{9}{8}x\dfrac{1}{3}=\dfrac{4}{25}+\dfrac{3}{8}\)

= \(\dfrac{4x8}{25x8}+\dfrac{25x3}{25x8}=\dfrac{32}{200}+\dfrac{75}{200}=\dfrac{107}{200}\)

\(2-\left(\dfrac{1}{7}x4+\dfrac{5}{21}\right)=2-\left(\dfrac{4}{7}+\dfrac{5}{21}\right)=2-\left(\dfrac{12}{21}+\dfrac{5}{21}\right)=2-\dfrac{17}{21}=\dfrac{42}{21}-\dfrac{17}{21}=\dfrac{25}{21}\)

   \(1\dfrac{7}{20}\div2,7+2,7\div1,35+\left(0,4\div2\dfrac{1}{2}\right)\times\left(4,2-1\dfrac{3}{40}\right)\)

\(=\dfrac{27}{20}\div\dfrac{27}{10}+\dfrac{27}{10}\div\dfrac{27}{20}+\left(\dfrac{2}{5}\div\dfrac{5}{2}\right)\times\left(\dfrac{21}{5}-\dfrac{43}{40}\right)\)

\(=\dfrac{27}{20}\times\dfrac{10}{27}+\dfrac{27}{10}\times\dfrac{20}{27}+\left(\dfrac{2}{5}\times\dfrac{2}{5}\right)\times\dfrac{25}{8}\)

\(=\dfrac{1}{2}+2+\dfrac{4}{25}\times\dfrac{25}{8}\)

\(=\dfrac{5}{2}+\dfrac{1}{2}\)

\(=3\)

\(\left(x+1\right)+\left(x+2\right)+...+\left(x+100\right)=5750\)

\(x+1+x+2+...+x+100=5750\)

\(\left(x+x+x+...+x\right)+\left(1+2+3+...+100\right)=5750\) 

Số số hạng là \(\left(100-1\right)\div1+1=100\) số hạng

=> Có 100 số x

Tổng là \(\left(100+1\right)\times100\div2=5050\) 

=> \(x\times100+5050=5750\) 

                 \(x\times100=5750-5050\) 

                 \(x\times100=700\) 

                           \(x=700\div100\) 

                           \(x=7\)

\(\left(x+1\right)+\left(x+2\right)+...+\left(x+100\right)=5750\)

\(\Rightarrow100x+\left(1+2+...100\right)=5750\)

\(\Rightarrow100x+\dfrac{100.\left(100+1\right)}{2}=5750\)

\(\Rightarrow100x+50.101=5750\)

\(\Rightarrow100x+5050=5750\)

\(\Rightarrow100x=5750-5050\)

\(\Rightarrow100x=700\)

\(\Rightarrow x=7\)

( \(\dfrac{1}{1}\)+\(\dfrac{1}{2}\)) :( \(\dfrac{1}{1}\)+\(\dfrac{1}{3}\)) : ( \(\dfrac{1}{ }1\)+\(\dfrac{1}{4}\))= \(\dfrac{2}{1}\):\(\dfrac{3}{1}\):\(\dfrac{4}{1}\)=2:3:4=0.16666666666

   \(\left(1+\dfrac{1}{2}\right)\div\left(1+\dfrac{1}{3}\right)\div\left(1+\dfrac{1}{4}\right)\)

\(=\dfrac{3}{2}\div\dfrac{4}{3}\div\dfrac{5}{4}\)

\(=\dfrac{3}{2}\times\dfrac{3}{4}\times\dfrac{4}{5}=\dfrac{9}{8}\times\dfrac{4}{5}=\dfrac{9}{10}\)

5/6 và 13/8 ( MC = 24 )

5/6 = 20/24

13/8= 39/ 24.

Ta thấy : \(\dfrac{5}{6}\) và \(\dfrac{13}{8}\) có MSCNN là 24

mà \(24\div6=4\) ; \(24\div8=3\) 

=> \(\dfrac{5}{6}=\dfrac{5\times4}{6\times4}=\dfrac{20}{24}\) ; \(\dfrac{13}{8}=\dfrac{13\times3}{8\times3}=\dfrac{39}{24}\)