a)3y(2y-4)-2y(3y+5)=44
6y2-12y-(6y2+10y)=44
6y2-12y-6y2-10y=44
-22y=44
y=-2
Vậy y=-2
b)(12x-5)(4x-1)+(3x-7)(1-16x)=81
48x2-12x-20x+5+3x-48x2-7+112x=81
          83x-2=81
          83x    =81+2
          83x    =83
              x=1
          Vậy x=1
                                     Đấy nhé bạn,nhớ k cho mình nha.<3

ĐỀ BÀI HƠI SAI SỬA LẠI:

Tìm x, y biết a) 3y(2y-4)-2y(3y+5)=44

                     b)(12x-5)(4x-1)+(3x-7)(1-16x)=81

Ta có: a chia cho 3 dư 1 ⇒ a = 3q + 1 (q ∈N)

b chia cho 3 dư 2 ⇒ b = 3k + 2 (k ∈N)

a.b = (3q +1)(3k + 2) = 9qk + 6q + 3k +2

Vì 9 ⋮ 3 nên 9qk ⋮ 3

Vì 6 ⋮ 3 nên 6q ⋮ 3

Vì 3⋮ 3 nên 3k ⋮ 3

Vậy a.b = 9qk + 6q + 3k + 2 = 3(3qk + 2q + k) +2 chia cho 3 dư 2.(đpcm)

Số tự nhiên a chia cho 5 dư 4, ta có: a = 5k + 4 (k ∈N)

Ta có: \(a^2\) = \(\left(5k+4\right)^2\)

      = 25\(k^2\) + 40k + 16

      = 25\(k^2\) + 40k + 15 + 1

      = 5(5\(k^2\)+ 8k +3) +1

Ta có: 5 ⋮ 5 nên 5(5\(k^2\) + 8k + 3) ⋮ 5

Vậy \(a^2\) = (5k+4)25k+42 chia cho 5 dư 1. (đpcm)

cảm ơn cậu nha

\(a,x+6x^2=0\)

=>  \(x\left(1+6x\right)=0\)

=>  \(\orbr{\begin{cases}x=0\\1+6x=0\Leftrightarrow6x=-1\Leftrightarrow x=-\frac{1}{6}\end{cases}}\)

\(b,2\left(x+3\right)-x\left(x+3\right)=0\)

=>  \(\left(2-x\right)\left(x+3\right)=0\)

=>  \(\orbr{\begin{cases}2-x=0\\x+3=0\end{cases}\Leftrightarrow\orbr{\begin{cases}x=2\\x=-3\end{cases}}}\)

\(c,5x\left(x-2\right)-\left(2-x\right)=0\)

=>  \(\left(5x+2\right)\left(x-2\right)=0\)

=>  \(\orbr{\begin{cases}5x+2=0\\x-2=0\end{cases}\Leftrightarrow\orbr{\begin{cases}x=-\frac{2}{5}\\x=2\end{cases}}}\)

\(d,\left(x+1\right)=\left(x+1\right)^2\)

=> \(\left(x+1\right)^2-\left(x+1\right)=0\)

=>   \(\left(x+1\right)\left(x+1-1\right)=0\)

=>  \(\orbr{\begin{cases}x+1=0\\x=0\end{cases}\Leftrightarrow\orbr{\begin{cases}x=-1\\x=0\end{cases}}}\)

\(a,75\cdot20,9+5^2\cdot20,9=20,9\left(75+25\right)=20,9\cdot100=2090\)

\(b,85\cdot12,7+5\cdot3\cdot12,7=12,7\left(85+15\right)=12,7\cdot100=1270\)

• a. 2090 b.1270

\(a,\frac{3}{7}x^2+6x+x^2y=x\left(\frac{3}{7}x+6+xy\right)\)

\(b,3x\left(x+3y\right)-6xy\left(x+3y\right)=3x\left(x+3y\right)\left(1-2y\right)\)

\(c,x\left(x+y\right)-5x-5y=x\left(x+y\right)-5\left(x+y\right)=\left(x-5\right)\left(x+y\right)\)

\(d,3\left(x-y\right)-5x\left(y-x\right)=\left(3+5x\right)\left(x-y\right)\)