lấy máy tính lưu ý : dạng 5 lít ý

7) 5x=4y ⇒\(\dfrac{x}{4}=\dfrac{y}{5}\)

Nhân cả hai vế với \(\dfrac{x}{4}\), ta có: \(\left(\dfrac{x}{4}\right)^2=\dfrac{x}{4}.\dfrac{y}{5}=\dfrac{xy}{20}=\dfrac{20}{20}=1\)

\(\left(\dfrac{x}{4}\right)^2=1\Rightarrow\left[{}\begin{matrix}\dfrac{x}{4}=1\\\dfrac{x}{4}=-1\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=4\\x=-4\end{matrix}\right.\)

⇒ \(\left[{}\begin{matrix}y=5\\y=-5\end{matrix}\right.\)

4) áp dụng tính chất dãy tỉ số bằng nhau ta có:

\(\dfrac{x}{0,5}=\dfrac{y}{0,3}=\dfrac{z}{0,2}=\dfrac{z-y+x}{0,2-0,3+0,5}=\dfrac{1}{\dfrac{2}{5}}=\dfrac{5}{2}\)

\(\dfrac{x}{0,5}=\dfrac{5}{2}\Rightarrow x=\dfrac{5}{4}\)

\(\dfrac{y}{0,3}=\dfrac{5}{2}\Rightarrow y=\dfrac{3}{4}\)

\(\dfrac{z}{0,2}=\dfrac{5}{2}\Rightarrow z=\dfrac{1}{2}\)

6) áp dụng tính chất dãy tỉ số bằng nhau ta có:

\(\dfrac{x+11}{13}=\dfrac{y+12}{14}=\dfrac{z+13}{15}=\dfrac{x+11+y+12+z+13}{13+14+15}=\dfrac{42}{42}=1\)

\(\dfrac{x+11}{13}=1\Rightarrow x=2\)

\(\dfrac{y+12}{13}=1\Rightarrow y=1\)

\(\dfrac{z+13}{15}=1\Rightarrow z=2\)

7) \(5x=4y\Rightarrow\dfrac{x}{4}=\dfrac{y}{5}=k\)

\(\Rightarrow x=4k,y=5k\)

\(x.y=20\\ \Rightarrow4k.5k=20\\ \Rightarrow20k^2=20\\ \Rightarrow k^2=1\\ \Rightarrow\left[{}\begin{matrix}k=-1\\k=1\end{matrix}\right.\)

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

\(y=5k\Rightarrow\left[{}\begin{matrix}y=-5\\y=5\end{matrix}\right.\)

Vậy \(\left(x,y\right)=\left\{\left(-4;-5\right);\left(4;5\right)\right\}\)

4/5 x 0,5 + 12/5 x 0,3 + 8 : 10 x 0,2

=4/5 x 0,5 + 12/5 x 0,3 + 4/5 x 0,2

=(4/5 + 12/5 + 4/5) x (0,5 + 0.3 + 0,2)

=4 x 1

=4

\(\frac{4}{5}x0,5+\frac{12}{5}x0,3+8:10x0,2=\)\(\frac{4}{5}x0,5+\frac{12}{5}x0,3+\frac{8}{10}x0,2=\)\(\frac{4}{5}x0,5+\frac{12}{5}x0,3+\frac{4}{5}x0,2=\)

\(=\frac{4}{5}x\left(0,5+0,2\right)+\frac{12}{5}x0,3\)\(=\frac{4}{5}x\frac{7}{10}+\frac{12}{5}x0,3=\frac{32}{25}\)

\(\frac{4}{5}\)x 0,5+ \(\frac{12}{5}\)x 0,3+ 8: 10x 0,2.

= 0,8x 0,5+ 2,4x 0.3+ 0,8x 0,2.

= 0,4+ 0,72+ 0,16.

= 1,12+ 0,16.

= 1,28.

a) 0,03

b) 3

c) 1,7

d) 1

1)

a)0,03

b)3

c)1,7

d)1

a) 0,03

b) 0,8

c) 1,7

d) 1

k Đúng Cho Mình Bạn Nhé.

a)1/2:0,5-1/4:0,25+1/8:0,125-1/10:0,1

=1/2x2-1/4x4+1/8x8-1/10x10

=1-1+1-1

=0

b)không biết k 2 cái là dc rồi

Bài 1: 

b) Ta có: \(D=\dfrac{-5}{10}\cdot\dfrac{-4}{10}\cdot\dfrac{-3}{10}\cdot...\cdot\dfrac{3}{10}\cdot\dfrac{4}{10}\cdot\dfrac{5}{10}\)

\(=\dfrac{-5}{10}\cdot\dfrac{-4}{10}\cdot\dfrac{-3}{10}\cdot...\cdot0\cdot...\cdot\dfrac{3}{10}\cdot\dfrac{4}{10}\cdot\dfrac{5}{10}\)

=0

0,2-0,375+5/11/-0,3+9/16-15/22