a, \(\dfrac{4}{7}\). \(\dfrac{a}{b}\) - \(\dfrac{1}{3}\) = \(\dfrac{1}{21}\)

     \(\dfrac{4}{7}\).\(\dfrac{a}{b}\)        =   \(\dfrac{1}{21}\) + \(\dfrac{1}{3}\)

     \(\dfrac{4}{7}\).\(\dfrac{a}{b}\)        = \(\dfrac{8}{21}\)

          \(\dfrac{a}{b}\)       = \(\dfrac{8}{21}\):\(\dfrac{4}{7}\)

           \(\dfrac{a}{b}\)      = \(\dfrac{2}{3}\)

b, \(\dfrac{a}{b}\) + \(\dfrac{2}{3}\).\(\dfrac{1}{3}\) = \(\dfrac{2}{3}\)

     \(\dfrac{a}{b}\) + \(\dfrac{2}{9}\) = \(\dfrac{2}{3}\)

      \(\dfrac{a}{b}\)        = \(\dfrac{2}{3}\) - \(\dfrac{2}{9}\)

       \(\dfrac{a}{b}\)       = \(\dfrac{4}{9}\)

c, \(\dfrac{a}{b}\) - \(\dfrac{1}{2}.\)\(\dfrac{2}{3}\) = \(\dfrac{2}{7}\)

    \(\dfrac{a}{b}\) - \(\dfrac{1}{3}\)     = \(\dfrac{2}{7}\)

    \(\dfrac{a}{b}\)           = \(\dfrac{2}{7}\) + \(\dfrac{1}{3}\)

    \(\dfrac{a}{b}\)          = \(\dfrac{13}{21}\)

d, \(\dfrac{11}{13}\): \(\dfrac{a}{b}\): \(\dfrac{2}{3}\) = 2\(\dfrac{7}{13}\)

     \(\dfrac{11}{13}\): \(\dfrac{a}{b}\):\(\dfrac{2}{3}\) = \(\dfrac{33}{13}\)

      \(\dfrac{11}{13}\): \(\dfrac{a}{b}\)    = \(\dfrac{33}{13}\) \(\times\) \(\dfrac{2}{3}\)

       \(\dfrac{11}{13}\): \(\dfrac{a}{b}\)   = \(\dfrac{66}{39}\)

                \(\dfrac{a}{b}\) = \(\dfrac{11}{13}\) : \(\dfrac{66}{39}\)

                 \(\dfrac{a}{b}\) = \(\dfrac{1}{2}\)

a) 4,6,8,10,12

B)5,10,15,20,25

a) 4,6,8,10,12

B)5,10,15,20,25

Bạn xem lại đề, phần diện tích.

\(\dfrac{1}{4}+\dfrac{8}{9}\le\dfrac{x}{36}\le1-\left(\dfrac{3}{8}-\dfrac{5}{6}\right)\\ \Rightarrow\dfrac{41}{36}\le\dfrac{x}{36}\le\dfrac{35}{24}\\ \Rightarrow\dfrac{82}{72}\le\dfrac{2x}{72}\le\dfrac{105}{72}\\ \Rightarrow41\le x< 51,5\)

\(\dfrac{1}{4}+\dfrac{8}{9}\le\dfrac{x}{36}< 1-\left(\dfrac{3}{8}-\dfrac{5}{6}\right)\)

\(\Rightarrow\dfrac{41}{36}\le\dfrac{x}{36}< 1-\left(-\dfrac{11}{24}\right)\)

\(\Rightarrow\dfrac{41}{36}\le\dfrac{x}{36}< 1+\dfrac{11}{24}\)

\(\Rightarrow\dfrac{41}{36}\le\dfrac{x}{36}< \dfrac{35}{24}\)

\(\Rightarrow\dfrac{82}{72}\le\dfrac{2x}{72}< \dfrac{105}{72}\)

\(\Rightarrow82\le2x< 105\)

\(\Rightarrow41\le x< \dfrac{105}{2}\)

\(\dfrac{1}{4}+\dfrac{8}{9}\le\dfrac{x}{36}< 1-\left(\dfrac{3}{8}-\dfrac{5}{6}\right)\)

\(\dfrac{\Leftrightarrow41}{36}\le\dfrac{x}{36}< \dfrac{35}{24}\)

\(\dfrac{\Leftrightarrow82}{72}\le\dfrac{2x}{72}< \dfrac{105}{72}\)

\(\Rightarrow82\le2x< 105\)

\(\Rightarrow x=\left\{41;42;43;44;45;46;47;48;49;50;51;52\right\}\)

Ta có x < 19,54 < y

\(\Rightarrow x=19,y=20\)

x = 19 

y = 20

\(xy+2x+2y=-16\)

\(\Rightarrow x\left(y+2\right)+2y+4-4=-16\)

\(\Rightarrow x\left(y+2\right)+2\left(y+2\right)=-12\)

\(\Rightarrow\left(y+2\right)\left(x+2\right)=-12\)

\(\Rightarrow\left(x+2\right);\left(y+2\right)\in B\left(12\right)=\left\{-1;1;-2;2;-3;3;-4;4;-6;6;-12;12\right\}\)

\(\Rightarrow\left(x;y\right)\in=\left\{\left(-3;10\right);\left(-1;-14\right);\left(-4;3\right);\left(0;-8\right);\left(-5;2\right);\left(1;2\right);\left(-6;1\right);\left(2;-5\right);\left(-8;0\right);\left(4;-4\right);\left(-14'-1\right);\left(10;-3\right)\right\}\)

\(\left(x+2\right);\left(y+2\right)\) không phải thuộc B(12) mà nó phải là 2 số nguyên có tích bằng 12 chứ em

a, (675 + 325) x 42

= 675 x 42 + 325 x 42

= 28350 + 13650

=42000

(675 + 325) x 42

= 1000 x 42

= 42000

b, 36 x ( 196 - 96)

= 36 x 100

 = 3600

36 x ( 196 - 96)

= 36 x 196 - 36 x 96

= 7056 - 3456 

= 3600

\(\dfrac{3}{5}\) = \(\dfrac{3\times11}{5\times11}\) = \(\dfrac{33}{55}\);         \(\dfrac{3}{4}\) = \(\dfrac{3\times11}{4\times11}\) = \(\dfrac{33}{44}\)

10 phân số lớn hơn \(\dfrac{3}{5}\) và bé hơn \(\dfrac{3}{4}\) là 10 phân số lớn hơn \(\dfrac{33}{55}\)và bé hơn \(\dfrac{33}{44}\). Đó lần lượt là các phân số:

                    \(\dfrac{33}{54};\dfrac{33}{53};\dfrac{33}{52};\dfrac{33}{52};\dfrac{33}{50};\dfrac{33}{49};\dfrac{33}{48};\dfrac{33}{47};\dfrac{33}{46};\dfrac{33}{45}\)