my/father/farmer

my father is a farmer

he/work/farm

he works on the farm

my/mother/house wife

my mother is a housewife

she/work/home/help/the farm

she works at home and help on the farm

my/brother/engineer

my brother is an engineer

he/work/factory

he works in the factory

Tìm trước khi hỏi nhé

\(\left(x+\dfrac{2}{3}\right)^2+\left(\dfrac{3}{2}-y\right)^2=0\)

Xét \(\left\{{}\begin{matrix}\left(x+\dfrac{2}{3}\right)^2\ge0\\\left(\dfrac{3}{2}-y\right)^2\ge0\end{matrix}\right.\)

\(\Rightarrow\)\(\left\{{}\begin{matrix}\left(x+\dfrac{2}{3}\right)^2=0\\\left(\dfrac{3}{2}-y\right)^2=0\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x=\dfrac{-2}{3}\\y=\dfrac{3}{2}\end{matrix}\right.\)

Bài 2:

Câu trả lời của bạn

Bài 1:

a) \(A=2x^2-4x+8\)

\(=2\left(x^2-2x+4\right)=2\left(x-2\right)^2\)

Xét \(2\left(x-2\right)^2\ge0\)

\(\Rightarrow Min_A=0\Leftrightarrow x=2\)

b) \(B=n^5-5n^3+4n\)

\(=n\left(n^4-5n^2+4\right)\)

\(=n\left(n^4-n^2-4n^2+4\right)\)

\(=n\left[n^2\left(n^2-1\right)-4\left(n^2-1\right)\right]\)

\(=n\left[\left(n^2-4\right)\left(n^2-1\right)\right]\)

\(=n\left[\left(n-2\right)\left(n+2\right)\left(n-1\right)\left(n+1\right)\right]\)

\(=\left(n-2\right)\left(n-1\right)n\left(n+1\right)\left(n+2\right)\)

Xét \(\left(n-2\right)\left(n-1\right)n\left(n+1\right)\left(n+2\right)\) là 5 số nguyên liên tiếp

\(\Rightarrow\)\(\left(n-2\right)\left(n-1\right)n\left(n+1\right)\left(n+2\right)⋮2;3;4;5\)

\(\Rightarrow\)\(\left(n-2\right)\left(n-1\right)n\left(n+1\right)\left(n+2\right)⋮120\)

\(\Rightarrow\)\(\left(n-2\right)\left(n-1\right)n\left(n+1\right)\left(n+2\right)⋮30\)

Cách 1:

Tổng số vở hai bạn đã mua là:

3 x 2 = 6 (quyển)

Gía tiền 1 quyển là:

72 000 : 6 = 12 000 (đồng)

Cách 2:

Vì mỗi bạn cùng mua 3 quyển vở cùng loại nên số tiền mỗi bạn phải trả là bằng nhau

Mỗi bạn phải trả số tiền là:

72 000 : 2 = 36 000 (đồng)

1 quyển sách có giá là:

36 000 : 3 = 12 000 (đồng)

cả hai trái đều không đau, chỉ có cái đầu đau thôi

a) \(x^2-4=0\)

\(\Rightarrow x^2-2^2=0\)

\(\Rightarrow\left(x-2\right)\left(x+2\right)=0\)

\(\Rightarrow\left[{}\begin{matrix}x-2=0\\x+2=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=2\\x=-2\end{matrix}\right.\)

b) \(x\left(x+5\right)=9x\)

\(\Rightarrow x^2+5x-9x=0\)

\(\Rightarrow x^2-4x=0\)

\(\Rightarrow x\left(x-4\right)=0\)

\(\Rightarrow\left[{}\begin{matrix}x=0\\x=4\end{matrix}\right.\)

c) \(3x^3-48x=0\)

\(\Rightarrow3x\left(x^2-16\right)=0\)

\(\Rightarrow\left[{}\begin{matrix}x=0\\x^2-16=0\Rightarrow\left(x-4\right)\left(x+4\right)=0\end{matrix}\right.\)

\(\Rightarrow\left[{}\begin{matrix}x-4=0\\x+4=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=4\\x=-4\end{matrix}\right.\)

d) \(x^4+x^2-20=0\)

\(\Rightarrow\left(x^2\right)^2+x^2-20=0\)

Đặt x² = a

\(\Rightarrow a^2+a-20=0\)

\(\Rightarrow a^2+5a-4a-20=0\)

\(\Rightarrow a\left(a+5\right)-4\left(a+5\right)=0\)

\(\Rightarrow\left(a-4\right)\left(a+5\right)=0\)

\(\Rightarrow\left(x^2-4\right)\left(x^2+5\right)=0\)

\(\Rightarrow\left[{}\begin{matrix}x^2-4=0\\x^2+5=0\end{matrix}\right.\)\(\Rightarrow\left[{}\begin{matrix}x^2=4\Rightarrow x=\pm2\\x^2=-5\Rightarrow x\in\varnothing\end{matrix}\right.\)

\(\left(2n+1\right)^3=27\)

\(\Rightarrow2n+1=3\)

\(\Rightarrow2n=2\Rightarrow n=1\)