Tính:
a/\(A=\left(-0,75-\dfrac{1}{4}\right):\left(-5\right)+\dfrac{1}{48}-\left(\dfrac{-1}{6}\right):\left(-3\right)\)
b/\(B=\left(\dfrac{6}{25}-1,24\right):\dfrac{3}{7}:\left[\left(3\dfrac{1}{2}-3\dfrac{2}{3}\right):\dfrac{1}{14}\right]\)
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Bài 1:
a. $=\frac{25-4}{12}=\frac{21}{12}=\frac{7}{4}$
b. $=\frac{-5}{4}+\frac{15}{4}=\frac{15-5}{4}=\frac{10}{4}=\frac{5}{2}$
c. $=\frac{-15}{12}+\frac{15}{12}+\frac{3}{-4}=\frac{-15+15}{12}+\frac{3}{-4}=\frac{3}{-4}$
d.
$=3+\frac{1}{4}-1-\frac{1}{3}=(3-1)-(\frac{1}{3}-\frac{1}{4})$
$=2-\frac{1}{12}=\frac{23}{12}$
e.
$=3,1-2,5+2,5-3,1=(3,1-3,1)-(2,5-2,5)=0-0=0$
g.
$=\frac{1}{18}-\frac{3}{4}+\frac{3}{4}-\frac{2}{5}$
$=\frac{1}{18}-\frac{2}{5}=\frac{-31}{90}$
Bài 2:
a.
$x+\frac{1}{5}=\frac{3}{7}$
$x=\frac{3}{7}-\frac{1}{5}=\frac{8}{35}$
b.
$x=\frac{1}{2}+\frac{3}{4}=\frac{2}{4}+\frac{3}{4}=\frac{5}{4}$
c.
$\frac{2}{5}+x=\frac{11}{12}-\frac{2}{3}=\frac{1}{4}$
$x=\frac{1}{4}-\frac{2}{5}=\frac{-3}{20}$
d.
$2x(x-\frac{1}{7})=0$
$\Rightarrow 2x=0$ hoặc $x-\frac{1}{7}=0$
$\Rightarrow x=0$ hoặc $x=\frac{1}{7}$
e.
$\frac{1}{4}:x=\frac{2}{5}-\frac{3}{4}=\frac{-7}{20}$
$x=\frac{1}{4}: \frac{-7}{20}=\frac{-5}{7}$
f.
$x=\frac{5}{12}-\frac{1}{3}=\frac{1}{12}$
\(S_{35}=1-2+3-4+...+35\)
\(\Rightarrow S_{35}=\left(-1\right)+\left(-1\right)+...+35=17.\left(-1\right)+35=18\)
\(S_{60}=1-2+3-4+...+60\)
\(\Rightarrow S_{60}=\left(-1\right)+\left(-1\right)+...+59-60=30.\left(-1\right)=-30\)
\(\Rightarrow S_{35}+S_{60}=18-30=-12\)
\(A=1999^{2000}+\dfrac{1}{1999^{1999}}+1\)
\(B=1999^{1999}+\dfrac{1}{1999^{1998}}+1\)
\(\Rightarrow A-B=1999^{1999}.\left(1999-1\right)+\dfrac{1}{1999^{1998}}.\left(\dfrac{1}{1998}-1\right)\)
\(\Rightarrow A-B=1998.1999^{1999}-\dfrac{1997}{1998}.\dfrac{1}{1999^{1998}}\)
mà \(0< \dfrac{1997}{1998}.\dfrac{1}{1999^{1998}}< 1;1998.1999^{1999}>0\)
\(\Rightarrow A-B=1998.1999^{1999}-\dfrac{1997}{1998}.\dfrac{1}{1999^{1998}}>0\)
\(\Rightarrow A>B\)
Trình bày rõ ràng và chi tiết vào ạ? Kết quả cũng sai mà ghi như tht v?
Diện tích thửa ruộng :
\(\dfrac{1}{2}.\left(15+20\right).5=87,5\) \(\left(m^2\right)\)
Số kg thóc thu hoạch :
\(87,5.0,6=52,5\) \(\left(kg\right)\)
Diện tích mảnh ruộng là:
1/2 . 5 ( 15 + 20 ) = 87,5(m2 )
Số kg thóc mạnh ruộng cho sản là:
0,6 . 87,5 = 52,5 ( kg )
Vậy ...
Gọi 3 số tự nhiên liên tiếp là x; x+1 ; x+2
Ta có:
x.(x+1) + 50 = (x+1).(x+2)
=> (x+1).(x+2) - x.(x+1) = 26
=> (x+1).(x+2-x) = 26
=> (x+1).2 = 26
=> x+1 = 26 : 2 = 13
\(-\dfrac{3}{5}:\left(-\dfrac{3}{4}\right)=\dfrac{3}{5}.\dfrac{4}{3}=\dfrac{4}{5}\)
\(-\dfrac{5}{2}:\left(-\dfrac{3}{4}\right)=\dfrac{5}{2}.\dfrac{4}{3}=\dfrac{10}{3}\)
\(x\left(1-3y\right)+1-3y-1=-4\)
\(\left(1-3y\right)\left(x+1\right)=-3\)
⇒ (x+1) và (1-3y) ϵ {-1;1;-3;3}
\(\Rightarrow\left(x;y\right)\in\left\{\left(-2;-\dfrac{2}{3}\right);\left(0;\dfrac{4}{3}\right);\left(-4;0\right);\left(2;\dfrac{2}{3}\right)\right\}\)
a) \(A=\left(-0,75-\dfrac{1}{4}\right):\left(-5\right)+\dfrac{1}{48}-\left(-\dfrac{1}{6}\right):\left(-3\right)\)
\(A=\left(-0,75-0,25\right):\left(-5\right)+\dfrac{1}{48}-\left(-\dfrac{1}{6}\right)\cdot\dfrac{-1}{3}\)
\(A=\left(-1\right):\left(-5\right)+\dfrac{1}{48}-\dfrac{1}{18}\)
\(A=\dfrac{1}{5}+\dfrac{1}{48}-\dfrac{1}{18}\)
\(A=\dfrac{119}{720}\)
b) \(B=\left(\dfrac{6}{25}-1,24\right):\dfrac{3}{7}:\left[\left(3\dfrac{1}{2}-3\dfrac{2}{3}\right):\dfrac{1}{14}\right]\)
\(B=\left(0,24-1,24\right):\dfrac{3}{7}:\left[\left(\dfrac{7}{2}-\dfrac{11}{3}\right):\dfrac{1}{14}\right]\)
\(B=-1:\dfrac{3}{7}:\left(-\dfrac{1}{6}:\dfrac{1}{14}\right)\)
\(B=-\dfrac{7}{3}:-\dfrac{7}{3}\)
\(B=1\)
a, A = (-0,75 - \(\dfrac{1}{4}\)) : (-5) + \(\dfrac{1}{48}\) - (- \(\dfrac{1}{6}\)) : (-3)
A = -(0,75 + 0,25): (-5) + \(\dfrac{1}{48}\) - \(\dfrac{1}{18}\)
A = -1 : (-5) + \(\dfrac{1}{48}\) - \(\dfrac{1}{18}\)
A = \(\dfrac{1}{5}\) + \(\dfrac{1}{48}\) - \(\dfrac{1}{18}\)
A = \(\dfrac{53}{240}\) - \(\dfrac{1}{18}\)
A = \(\dfrac{119}{720}\)
b, B = (\(\dfrac{6}{25}\) - 1,24): \(\dfrac{3}{7}\): [(3\(\dfrac{1}{2}\) - 3\(\dfrac{2}{3}\)): \(\dfrac{1}{14}\)]
B = (0,24 - 1,24): \(\dfrac{3}{7}\):[(\(\dfrac{7}{2}\)-\(\dfrac{11}{3}\)): \(\dfrac{1}{14}\)]
B = -1: \(\dfrac{3}{7}\):[ (-\(\dfrac{1}{6}\) : \(\dfrac{1}{14}\))]
B = -1: \(\dfrac{3}{7}\): (- \(\dfrac{7}{3}\))
B = 1 \(\times\) \(\dfrac{7}{3}\) \(\times\) \(\dfrac{3}{7}\)
B = 1