rút gọn
\(\dfrac{102}{80}\)
rút gọn phân số \(\dfrac{102}{80}\)
\(\dfrac{102}{80}=\dfrac{102:2}{80:2}=\dfrac{51}{40}\)
Rút gọn rồi tính:
\(\dfrac{70}{80}-\dfrac{2}{16}-\dfrac{3}{24}\)
\(\dfrac{70}{80}-\dfrac{2}{16}-\dfrac{3}{24}\)
\(=\dfrac{7}{8}-\dfrac{1}{8}-\dfrac{1}{8}=\dfrac{5}{8}\)
a) Số?
\(\dfrac{12}{18}=\dfrac{6}{?}=\dfrac{?}{3}\)
b) Rút gọn các phân số: \(\dfrac{12}{48}\); \(\dfrac{80}{100}\); \(\dfrac{75}{125}\).
a) Số:
\(\dfrac{12}{18}\) = \(\dfrac{6}{9}\) = \(\dfrac{2}{3}\)
b) Rút gọn các phân số:
\(\dfrac{12}{48}\) = \(\dfrac{1}{4}\)
\(\dfrac{80}{100}\)= \(\dfrac{4}{5}\)
\(\dfrac{75}{125}\) = \(\dfrac{3}{5}\)
Rút gọn: A = \(\dfrac{17^{100}+17^{96}+17^{92}+...+17^4+1}{17^{102}+17^{100}+17^{98}+...+17^2+1}\)
\(A=\dfrac{17^{100}+17^{96}+17^{92}+....+17^4+1}{17^{102}+17^{100}+17^{98}+....+17^2+1}\)
Gọi \(17^{100}+17^{96}+17^{92}+....+17^4+1\) là B
\(B=17^{100}+17^{96}+17^{92}+....+17^4+1\\ 17^4\cdot B=17^{104}+17^{100}+17^{96}+......+17^8+17^4\\ 17^4\cdot B-B=\left(17^{104}+17^{100}+17^{96}+......+17^8+17^4\right)-\left(17^{100}+17^{96}+17^{92}+....+17^4+1\right)\\ B\cdot\left(17^4-1\right)=17^{104}-1\\ B=\dfrac{17^{104}-1}{17^4-1}\)
Gọi \(17^{102}+17^{100}+17^{98}+....+17^2+1\) là C
\(C=17^{102}+17^{100}+17^{98}+....+17^2+1\\ C\cdot17^2=17^{104}+17^{102}+17^{100}+17^{98}+....+17^2\\ C\cdot17^2-C=\left(17^{104}+17^{102}+17^{100}+17^{98}+....+17^2\right)-\left(17^{102}+17^{100}+17^{98}+....+17^2+1\right)\\ C\cdot\left(17^2-1\right)=17^{104}-1\\ C=\dfrac{17^{104}-1}{17^2-1}\)
=>
\(A=B:C\\ A=\dfrac{17^{104}-1}{17^4-1}:\dfrac{17^{104}-1}{17^2-1}\\ A=\dfrac{17^2-1}{17^4-1}\)
A = \(\dfrac{T}{M}\)
M = T + (\(17^{102}+17^{98}+17^{94}+...+17^2\))
M = T + \(17^2\left(17^{100}+17^{96}+17^{92}+...+17^0\right)\)
M = T + \(17^2\cdot\) T = T(\(1+17^2\))
=> A = \(\dfrac{T}{T\left(1+17^2\right)}=\dfrac{1}{1+17^2}\)
rút gọn phân số:
\(a.\dfrac{-315}{540}\)
\(b.\dfrac{25.13}{26.35}\)
\(c.\dfrac{3.13-13.18}{15.40-80}\)
\(d.\dfrac{-1997.1996+1}{\text{(}-1995\text{)}.\left(-1997\right)+1996}\)
rút gọn biểu thức : \(\dfrac{5-2\sqrt{5}}{\sqrt{5}}\) - ( \(5\sqrt{5}-3\) ) + \(\sqrt{80}\)
\(\dfrac{5-2\sqrt{5}}{\sqrt{5}}-\left(5\sqrt{5}-3\right)+\sqrt{80}\\ =\dfrac{\sqrt{5}\left(\sqrt{5}-2\right)}{\sqrt{5}}-5\sqrt{5}+3+4\sqrt{5}\\ =\sqrt{5}-2-5\sqrt{5}+3+4\sqrt{5}\\ =\sqrt{5}\left(1-5+4\right)-2+3\\ =0+1\\ =1\)
\(=\sqrt{5}-2-5\sqrt{5}+3+4\sqrt{5}=1\)
Thực hiện phép tính (rút gọn biểu thức)
a)\(\sqrt{20}\)-3\(\sqrt{45}\)-\(\dfrac{1}{2}\sqrt{80}\)
b) 12\(\sqrt{54}\)-\(\dfrac{2}{5}\)\(\sqrt{150}\)+3\(\sqrt{24}\)
Lời giải:
a.
$=2\sqrt{5}-9\sqrt{5}-2\sqrt{5}=(2-9-2)\sqrt{5}=-9\sqrt{5}$
b.
$=36\sqrt{6}-2\sqrt{6}+6\sqrt{6}=(36-2+6)\sqrt{6}=40\sqrt{6}$
Rút gọn phân số:
a) \(\dfrac{2929-101}{2.1149+404}\)
b) \(\dfrac{6.9-2.17}{63.3-119}\)
c) \(\dfrac{3.13-13.18}{15.40-80}\)
d) \(\dfrac{-1997-1996+1}{\left(-1995\right).\left(-1997\right)+1996}\)
e) \(\dfrac{2.3+4.6+14.21}{3.5+6.10+21.35}\)
g) \(\dfrac{\left(-5\right)^3.40.4^3}{135.\left(-3\right)^{14}.\left(-100\right)^0}\)
h) \(\dfrac{18.34+\left(-18\right).124}{-36.17+9.\left(52\right)}\)
j) \(\dfrac{9.11+32.9}{23.15+12.23}\)
k) \(\dfrac{12.13+24.26+36.39}{24.26+48.52+72.78}\)
b) \(\dfrac{6\cdot9-2\cdot17}{63\cdot3-119}\)
\(=\dfrac{2\left(3\cdot9-17\right)}{7\cdot\left(3\cdot9-17\right)}\)
\(=\dfrac{2}{7}\)
rút gọn
a)\(\sqrt{20}\)+\(\sqrt{80}\)-\(\sqrt{45}\)
b)4.\(\sqrt{\dfrac{2}{9}}\)+\(\sqrt{2}\)+\(\sqrt{\dfrac{1}{18}}\)
c)\(\dfrac{1}{\sqrt{3}-1}\)-\(\dfrac{1}{\sqrt{3}+1}\)
d)\(\dfrac{1}{\sqrt{x}-1}\)-\(\dfrac{1}{\sqrt{x}+1}\)+1
e)\(\sqrt{x}\)-2+\(\dfrac{10-x}{\sqrt{x}+2}\)
g)\(\dfrac{1}{\sqrt{x}+2}\)-\(\dfrac{2}{\sqrt{x}-2}\)-\(\dfrac{\sqrt{x}}{4-x}\)