\(\left(y+1\right)+\left(Y+3\right)+...+\left(y+99\right)=2550\)
\(\left(y+y+..+y\right)+\left(1+3+5+...+99\right)\)
\(50y+\frac{\left(99+1\right).50}{2}=2550\)
\(50y+2500=2550\)
\(\Rightarrow50y=50\)
\(\Rightarrow y=50:50=1\)

\(\Rightarrow y+y+...+y+1+3+...+99=2550\Rightarrow50y+\frac{\left(99+1\right)\cdot50}{2}=2550\)

\(\Rightarrow50y+2500=2550\Rightarrow50y=50\Rightarrow y=1\)

a) 186 - 3 x y = 99

            3 x y = 186 - 99

            3 x y = 87

                 y = 87/3

b) y :2 + y:3 + y:4 = 15

   y x 1/2 + y x 1/3 + y x 1/4 = 15

y x ( 1/2 + 1/3 + 1/4) =15

y x 13/12                 = 15

y                             = 15 : 13/12

y                             = 180/13

Tìm y biết

a 186 -3 x y = 99

          3 x y = 186 - 99 

        3 x y    = 87

           y      = 87 : 3 

       y          =  29

b y :2 + y : 3 + y : 4 = 15

 \(\frac{y}{2}+\frac{y}{3}+\frac{y}{4}=15\)

\(\frac{6\times y}{12}+\frac{4\times y}{12}+\frac{3\times y}{12}=\frac{180}{12}\)

\(6\times y+4\times y+3\times y=180\)

\(\left(6+4+3\right)\times y=180\)

\(13\times y=180\)

\(y=180:13\)

\(y=\frac{180}{13}\)

MÌNH GHI RA TỪNG CHI TIẾT RỒI NHA , CHÚC BẠN HỌC TỐT !!! 

a,186-3xy=99

 3xy=186-99

3xy=87

y=87:3

y=29

1.
\(\left(\frac{3}{1\times3}+\frac{3}{3\times5}+\frac{3}{5\times7}+...+\frac{3}{97\times99}\right)-x:\frac{3}{2}=\frac{7}{3}\\ \left(\frac{2}{1\times3}+\frac{2}{3\times5}+\frac{2}{5\times7}+...+\frac{2}{97\times99}\right):\frac{3}{2}-x:\frac{3}{2}=\frac{7}{3}\\\left[\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{97}-\frac{1}{99}\right)-x\right]:\frac{3}{2}=\frac{7}{3}\\ \left(1-\frac{1}{99}\right)-x=\frac{7}{3}\times\frac{3}{2}\\ \frac{98}{99}-x=\frac{7}{2}\\ x=\frac{98}{99}-\frac{7}{2}=\frac{-497}{198}\)

2.\(\frac{x}{y}=\frac{4}{3}\Rightarrow\hept{\begin{cases}x=4a\\y=3a\\x-y=4a-3a=a\end{cases}}\\ \left(x-y\right)^{2015}=5^{2015}\Rightarrow x-y=5\\ \Rightarrow a=5\Rightarrow\hept{\begin{cases}x=4\times5=20\\y=3\times5=15\end{cases}}\)

1.

Đặt \(.K=\frac{x+99}{-1}=\frac{y-98}{2}=\frac{z+97}{-3}\)

\(\Rightarrow\frac{x+97}{K}=-1\)

\(\Rightarrow\frac{y-98}{K}=2\)

\(\Rightarrow\frac{z+97}{K}=-3\)

\(\Rightarrow\frac{x+99}{K}+\frac{y-98}{K}+\frac{z+97}{K}=\left(-1\right)+2+\left(-3\right)\)

\(\Rightarrow\frac{\left(x+99\right)+\left(y-98\right)+\left(z+97\right)}{K}=-2\)

Đến đây thì ... mình quên mất tiêu rồi bạn tự nghĩ tiếp nha :)

Ta có : x = 1.2 + 2.3 + 3.4 + ... + 99.100

              = 1.(1 + 1) + 2.(2 + 1) + ... + 99.(99 + 1)

              = 1.1 + 1 + 2.2 + 2 + ... + 99.99 + 99

              = (1.1 + 2.2 + 3.3 + ... + 99.99) + (1 + 2 + 3 + ... + 99)

              = y + 99.(99 + 1) : 2

              = y + 99.50

              = y + 4950

=> x = y + 4950

=> x - y = 4950 

Vậy x - y = 4950 

bn nhân 3 vào x và y rồi l x - y là s

\(\frac{x+99}{-1}=\frac{y-98}{2}=\frac{z+97}{-3}=\frac{x+99-\left(y-98\right)+\left(z+97\right)}{-1-2+\left(-3\right)}=\frac{\left(x-y+z\right)+294}{-6}=\frac{50+294}{-6}=-\frac{172}{3}\)

x + 99 = 172/3  => x =-125/3

y - 98 = - 344/3 => y =  - 50 /3

z+ 97 = 172 => z = 75