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\(...=-\dfrac{4}{7}-\dfrac{3}{11}+\dfrac{3}{11}-\dfrac{3}{7}=-\dfrac{4}{7}-\dfrac{3}{7}=-1\)
-(4/7 + 3/11) - (-3/11 + 3/7)
= (-4/7) + (-3/11) - (-3/11) - 3/7
= [(-4/7) - 3/7)] + [(-3/11) - (-3/11)]
= -1 + 0
= -1
1: A=-1/2*xy^3*4x^2y^2=-2x^3y^5
Bậc là 8
Phần biến là x^3;y^5
Hệ số là -2
2:
a: P(x)=3x+4x^4-2x^3+4x^2-x^4-6
=3x^4-2x^3+4x^2+3x-6
Q(x)=2x^4+4x^2-2x^3+x^4+3
=3x^4-2x^3+4x^2+3
b: A(x)=P(x)-Q(x)
=3x^4-2x^3+4x^2+3x-6-3x^4+2x^3-4x^2-3
=3x-9
A(x)=0
=>3x-9=0
=>x=3
Gọi thời gian của T,D,M lần lượt là \(a,b,c(giờ;a,b,c>0)\)
Áp dụng tc dtsbn:
\(10a=9b=8c\Leftrightarrow\dfrac{10a}{360}=\dfrac{9b}{360}=\dfrac{8c}{360}\Leftrightarrow\dfrac{a}{36}=\dfrac{b}{40}=\dfrac{c}{45}=\dfrac{c-a}{45-36}=\dfrac{0,3}{9}=\dfrac{1}{30}\\ \Leftrightarrow\left\{{}\begin{matrix}a=\dfrac{6}{5}\\b=\dfrac{4}{3}\\c=\dfrac{3}{2}\end{matrix}\right.\)
Vậy ...
\(\text{Bài 1:a)}25\dfrac{3}{19}.\left(-\dfrac{4}{5}\right)-35\dfrac{3}{19}.\left(-\dfrac{4}{5}\right)\)
\(=\dfrac{478}{19}.\left(-\dfrac{4}{5}\right)-\dfrac{668}{19}.\left(-\dfrac{4}{5}\right)\)
\(=\left(-\dfrac{4}{5}\right).\left(\dfrac{478}{19}-\dfrac{668}{19}\right)\)
\(=\left(-\dfrac{4}{5}\right).\left(\dfrac{-190}{19}\right)\)
\(=\left(-\dfrac{4}{5}\right).\left(-10\right)=8\)
\(\text{b)}5:\left(-\dfrac{5}{2}\right)^2+\dfrac{2}{15}.\sqrt{\dfrac{9}{4}}-\left(-2021\right)^0+0,25\)
\(=5:\dfrac{25}{4}+\dfrac{2}{15}.\dfrac{3}{2}-1+\dfrac{1}{4}\)
\(=\dfrac{4}{5}+\dfrac{1}{5}-1+\dfrac{1}{4}\)
\(=1-1+\dfrac{1}{4}\)
\(=0+\dfrac{1}{4}=\dfrac{1}{4}\)
\(\text{Bài 2:a)}\dfrac{8}{5}-\dfrac{3}{5}:x=0,4\)
\(\dfrac{3}{5}:x=\dfrac{8}{5}-0,4=\dfrac{6}{5}\)
\(x=\dfrac{3}{5}.\dfrac{5}{6}=\dfrac{1}{2}\)
\(\text{b)}\left(3x-\dfrac{1}{2}\right)^2+\dfrac{21}{25}=1\)
\(\left(3x-\dfrac{1}{2}\right)^2\) \(=1-\dfrac{21}{25}=\dfrac{4}{25}=\pm\left(\dfrac{2}{5}\right)^2\)
\(\text{Vậy }3x-\dfrac{1}{2}=\dfrac{2}{5}\)
\(3x\) \(=\dfrac{2}{5}+\dfrac{1}{2}=\dfrac{9}{10}\)
\(x\) \(=\dfrac{9}{10}.\dfrac{1}{3}=\dfrac{3}{10}\)
\(\text{hoặc }3x-\dfrac{1}{2}=\dfrac{-2}{5}\)
\(3x\) \(=\left(\dfrac{-2}{5}\right)+\dfrac{1}{2}=\dfrac{1}{10}\)
\(x\) \(=\dfrac{1}{10}.\dfrac{1}{3}=\dfrac{1}{30}\)
\(\Rightarrow x\in\left\{\dfrac{3}{10};\dfrac{1}{30}\right\}\)
Bài 2:
a: =>3/5:x=6/5
hay x=3/5:6/5=1/2
b: \(\Leftrightarrow\left(3x-\dfrac{1}{2}\right)^2=\dfrac{4}{5}\)
\(\Leftrightarrow\left[{}\begin{matrix}3x-\dfrac{1}{2}=\dfrac{2}{5}\\3x-\dfrac{1}{2}=-\dfrac{2}{5}\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{3}{10}\\x=\dfrac{1}{30}\end{matrix}\right.\)
Bài 2:
Chu vi hình chữ nhật:
\(\left(4\dfrac{3}{7}+2\dfrac{1}{5}\right).2=\left(\dfrac{31}{7}+\dfrac{11}{5}\right).2=\dfrac{232}{35}.2=\dfrac{464}{35}\left(m\right)\)
Diện tích hình chữ nhật:
\(4\dfrac{3}{7}.2\dfrac{1}{5}=\dfrac{31}{7}.\dfrac{11}{5}=\dfrac{341}{35}\left(m^2\right)\)