a, bạn viết rõ đề ra nhé 

b, \(\Rightarrow xy=35\Rightarrow x;y\inƯ\left(35\right)=\left\{\pm1;\pm5;\pm7;\pm35\right\}\)

1+1=3 

A nha em

Chọn A

A

hình chỉ là tham khỏa thôi nhá

a) Ta có: \(\dfrac{x}{3}=\dfrac{7}{y}\)

nên xy=21

b) Ta có: \(\dfrac{x}{y}=\dfrac{1}{6}\)

nên y=6x

c) Ta có: \(\dfrac{x}{7}=\dfrac{y}{-3}\)

nên -3x=7y

\(a,\dfrac{242}{363}+\dfrac{1616}{2121}=\dfrac{2}{7}\times y\)

\(\dfrac{2}{7}\times y=\dfrac{2\times121}{3\times121}+\dfrac{16\times101}{21\times101}\)

\(\dfrac{2}{7}\times y=\dfrac{2}{3}+\dfrac{16}{21}\)

\(\dfrac{2}{7}\times y=\dfrac{14}{21}+\dfrac{16}{21}\)

\(\dfrac{2}{7}\times y=\dfrac{30}{21}\)

\(\dfrac{2}{7}\times y=\dfrac{10}{7}\)

\(y=\dfrac{10}{7}:\dfrac{2}{7}\)

\(y=\dfrac{10}{7}\times\dfrac{7}{2}\)

\(y=5\)

\(---\)

\(b,\left(y+\dfrac{1}{4}\right)+\left(y+\dfrac{1}{16}\right)+\left(y+\dfrac{1}{16}\right)=2\)

\(\left(y+y+y\right)+\left(\dfrac{1}{4}+\dfrac{1}{16}+\dfrac{1}{16}\right)=2\)

\(3\times y+\left(\dfrac{4}{16}+\dfrac{2}{16}\right)=2\)

\(3\times y+\dfrac{6}{16}=2\)

\(3\times y+\dfrac{3}{8}=2\)

\(3\times y=2-\dfrac{3}{8}\)

\(3\times y=\dfrac{16}{8}-\dfrac{3}{8}\)

\(3\times y=\dfrac{13}{8}\)

\(y=\dfrac{13}{8}:3\)

\(y=\dfrac{13}{8}\times\dfrac{1}{3}\)

\(y=\dfrac{13}{24}\)

#\(Toru\)

` 242/363 + 1616/2121 = 2/7 xxy`

`2/7 xxy= 2/3 + 16/21`

`2/7 xxy= 14/21 +16/21`

`2/7 xxy= 30/21`

`y=10/7 : 2/7`

`y=10/7 xx 7/2`

`y=70/14`

`y=5`

__

` (y + 1/4) + (y + 1/16) + (y + 1/16) =2`

`(y+y+y)+(1/4 + 1/16+1/16)=2`

`3y + (4/16 +1/16 +1/16)=2`

`3y + 6/16=2`

`3y=2-6/16`

`3y= 32/16-6/16`

`3y= 26/16`

`y=26/16 : 3`

`y=26/48`

`y=13/24`

a,Ta có:

\(\dfrac{x}{y}=\dfrac{7}{4}=\dfrac{x}{7}=\dfrac{y}{4}\)

ÁP dụng tcdtsbn , ta có:

\(\dfrac{x}{7}=\dfrac{y}{4}=\dfrac{x+y}{7+4}=\dfrac{33}{11}=3\)

\(\Rightarrow\left\{{}\begin{matrix}x=21\\y=12\end{matrix}\right.\)

b,

\(\Rightarrow3.\left(x-1\right)=-24\)

\(\Rightarrow x-1=-8\)

\(\Rightarrow x=-7\)

A)\(\dfrac{x}{y}=\dfrac{7}{4}\Rightarrow\dfrac{x}{7}=\dfrac{y}{4}\)

Áp dụng t/c dtsbn ta có:

\(\dfrac{x}{7}=\dfrac{y}{4}=\dfrac{x+y}{7+4}=\dfrac{33}{11}=3\)

\(\dfrac{x}{7}=3\Rightarrow x=21\\ \dfrac{y}{4}=3\Rightarrow y=12\)

B) \(3\left(x-1\right)+5=-19\\ \Rightarrow3\left(x-1\right)=-24\\ \Rightarrow x-1=-8\\ \Rightarrow x=-7\)

\(x^2+y^2=\left(x+y\right)^2-2xy=\left(-8\right)^2-2\cdot15=34\)

Chọn D.

nhầm d nha

D

\(a)\)

\(y\times15-y\times25+y\times15=3780-255\)

\(y\times15-y\times25+y\times15=3525\)

\(y\times\left(15-25+15\right)=3525\)

\(y\times5=3525\)

\(y=3525:5\)

\(y=705\)

\(b)\)

\(341 + 448 : y - 141 = 214\)

\(341 + 448 : y = 214+141\)

\(341 + 448 : y = 355\)

\(448:y=355-341\)

\(448:y=14\)

\(y=448:14\)

\(y=32\)

a) y x 42 + y x 57 + y = 25 400

y x ( 42 + 57 + 1 ) = 25 400

y x 100 = 25 400

y = 25 400 : 100

y = 254

b) 142 x y - 41 x y - y = 408 000

y x ( 142 - 41 - 1 ) = 408 000

y x 100 = 408 000

y = 408 000 : 100

y = 4 080

a.y*(42+57+1)=25400

y*100=25400

y=25400:100=254

b.(142-41-1)*y=408000

100*y=408000

y=408000:100=4080

a. y x 42 + y x 57 + y = 25400

    y                             = 25400 : (42 + 57 + 1)

    y                             = 25400 : 100

    y                             = 254.

b. 142 x y - 41 x y - y = 408000

     y                            = 408000 : (142 - 41 - 1)

     y                            = 408000 : 100

     y                            = 4080.

\(\frac{x}{y}=\frac{7}{13}\Rightarrow\frac{x}{7}=\frac{y}{13}\) 

Áp dụng tính chất dãy tỉ số bằng nhau ta có : 

\(\frac{x}{7}=\frac{y}{13}=\frac{x+y}{7+13}=-\frac{60}{20}=-3\)

Suy ra : \(\frac{x}{7}=-3\Rightarrow x=-3.7=-21\)

\(\frac{y}{13}=-3\Rightarrow y=-3.13=-39\)

vay  : x=-21 va y=-39

------------------------------------------------

\(\frac{x}{16}=\frac{y}{21}\Rightarrow\frac{2x}{32}=\frac{y}{21}\)

Áp dụng tính chất dãy tỉ số bằng nhau ta có : 

\(\frac{2x}{32}=\frac{y}{21}=\frac{2x-y}{32-21}=\frac{34}{11}=?\)

sai de ko