bài 1:
Cho \(\dfrac{1}{a}+\dfrac{1}{b}+\dfrac{1}{c}=\dfrac{1}{a+b+c}\) .Chứng minh rằng:
\(\dfrac{1}{a^{1995}}+\dfrac{1}{b^{1995}}+\dfrac{1}{c^{1995}}=\dfrac{1}{a^{1995}+b^{1995}+c^{1995}}\)
Cho \(\dfrac{1}{a}+\dfrac{1}{b}+\dfrac{1}{c}=\dfrac{1}{a+b+c}\) .CMR:
\(\dfrac{1}{a^{1995}}+\dfrac{1}{b^{1995}}+\dfrac{1}{c^{1995}}=\dfrac{1}{a^{1995}+b^{1995}+c^{1995}}\)
HELP ME !
Xuất phát từ giả thiết , ta có :
\(\dfrac{1}{a}+\dfrac{1}{b}+\dfrac{1}{c}=\dfrac{1}{a+b+c}\)
=> \(\dfrac{bc+ac+ab}{abc}=\dfrac{1}{a+b+c}\)
=> \(\left(a+b+c\right)\left(ab+bc+ac\right)=abc\)
=> \(\left(a+b+c\right)\left(ab+bc+ac\right)-abc=0\)
=> \(a\left(ab+bc+ac\right)+b\left(ab+bc+ac\right)+c\left(ab+bc+ac\right)-abc=0\)=> a2b + abc + a2c + ab2 + b2c + abc + abc + bc2 + ac2 - abc = 0
=> ab(a + b) + ac( a + c) + bc( b + c) + 2abc = 0
=> ab( a + b + c) + ac( a + b + c ) + bc( b + c) = 0
=> ( a + b + c)a( b + c) + bc( b + c) = 0
=> ( b + c)( a2 + ab + ac + bc) = 0
=> ( b + c)( a + b)( c + a) = 0
Suy ra :
* b = -c
*a = -b
* c = -a
TH1 :Với b = -c
\(VT=\dfrac{1}{a^{1995}}+\dfrac{1}{\left(-c\right)^{1995}}+\dfrac{1}{c^{1995}}=\dfrac{1}{a^{1995}}\)
\(VP=\dfrac{1}{a^{1995}+b^{1995}+c^{1995}}=\dfrac{1}{a^{1995}+\left(-c\right)^{1995}+c^{1995}}=\dfrac{1}{a^{1995}}=VT\)
TH2 : với a = -b
\(VT=\dfrac{1}{\left(-b\right)^{1995}}+\dfrac{1}{b^{1995}}+\dfrac{1}{c^{1995}}=\dfrac{1}{c^{1995}}\)
\(VP=\dfrac{1}{a^{1995}+b^{1995}+c^{1995}}=\dfrac{1}{\left(-b\right)^{1995}+b^{1995}+c^{1995}}=\dfrac{1}{c^{1995}}=VT\)
TH3 . c = -a , Tương tự
Vậy , đẳng thức được Chứng minh
rút gọn phân số:
\(a.\dfrac{-315}{540}\)
\(b.\dfrac{25.13}{26.35}\)
\(c.\dfrac{3.13-13.18}{15.40-80}\)
\(d.\dfrac{-1997.1996+1}{\text{(}-1995\text{)}.\left(-1997\right)+1996}\)
so sánh các số hữu tỉ sau bằng cách hợp lí:
a) -0,2; \(\dfrac{1}{1000}\)
b) \(\dfrac{\text{13}}{\text{-35}};\dfrac{\text{-11}}{\text{28}}\)
c) \(\dfrac{2022}{-2021};\dfrac{-1995}{1996}\)
d) \(\dfrac{\text{-18}}{\text{13}};\dfrac{\text{181818}}{\text{131313}}\)
Cô làm rồi em nhé:
https://olm.vn/cau-hoi/giup-em-voiii.8161766187032
1.thực hiện phép tính
a.3990-(463 x72 -39 x 39):15 b.1995-321x3-6020:35
c.\(3-\dfrac{7}{11}\) d.\(\dfrac{1}{4}:\dfrac{1}{6}+5\)
a: =3990-(463*72-39^2):15
=3990-2121=1869
b: =1995-963-172=860
c: =33/11-7/11=26/11
d: =3/2+5=13/2
`@` `\text {Answer}`
`\downarrow`
`a,`
`3990 - (463 \times 72 - 39 \times 39) \div 15`
`= 3990 - (33336 - 1521) \div 15`
`= 3990 - 31815 \div 15`
`= 3990 - 2121`
`= 1869`
`b,`
`1995 - 321 \times 3 - 6020 \div 35`
`= 1995 - 963 - 172`
`= 1032 - 172`
`= 860`
`c,`
`3 - 7/11`
`= 33/11 - 7/11`
`= 26/11`
`d,`
`1/4 \div 1/6 + 5`
`= 1/4 \times 6 + 5`
`= 3/2 + 5`
`= 13/2`
giải các phương Trình sau
a) \(\left(\dfrac{x+2}{98}+1\right)+\left(\dfrac{x+3}{97}+1\right)=\left(\dfrac{x+4}{96}+1\right)+\left(\dfrac{x+5}{95}+1\right)\)
b) \(\dfrac{x+1}{1998}+\dfrac{x+2}{1997}=\dfrac{x+3}{1996}+\dfrac{x+4}{1995}\)
c) \(\dfrac{201-x}{99}+\dfrac{203-x}{97}+\dfrac{205-x}{95}+3=0\)
a) \(\left(\dfrac{x+2}{98}+1\right)+\left(\dfrac{x+3}{97}+1\right)=\left(\dfrac{x+4}{96}+1\right)+\left(\dfrac{x+5}{95}+1\right)\)
\(\Rightarrow\dfrac{x+100}{98}+\dfrac{x+100}{97}=\dfrac{x+100}{96}+\dfrac{x+100}{95}\)
\(\Rightarrow\dfrac{x+100}{98}+\dfrac{x+100}{97}-\dfrac{x+100}{96}-\dfrac{x+100}{95}=0\)
\(\Rightarrow\left(x+100\right)\left(\dfrac{1}{98}+\dfrac{1}{97}-\dfrac{1}{96}-\dfrac{1}{95}\right)=0\)
Vì \(\dfrac{1}{98}+\dfrac{1}{97}-\dfrac{1}{96}-\dfrac{1}{95}\ne0\) nên \(x+100=0\Leftrightarrow x=-100\)
b) \(\dfrac{x+1}{1998}+\dfrac{x+2}{1997}=\dfrac{x+3}{1996}+\dfrac{x+4}{1995}\)
\(\Rightarrow\dfrac{x+1}{1998}+1+\dfrac{x+2}{1997}+1=\dfrac{x+3}{1996}+1+\dfrac{x+4}{1995}+1\)
\(\Rightarrow\dfrac{x+1999}{1998}+\dfrac{x+1999}{1997}=\dfrac{x+1999}{1996}+\dfrac{x+1999}{1995}\)
\(\Rightarrow\dfrac{x+1999}{1998}+\dfrac{x+1999}{1997}-\dfrac{x+1999}{1996}-\dfrac{x+1999}{1995}=0\)
\(\Rightarrow\left(x+1999\right)\left(\dfrac{1}{1998}+\dfrac{1}{1997}-\dfrac{1}{1996}-\dfrac{1}{1995}\right)=0\)
Vì \(\dfrac{1}{1998}+\dfrac{1}{1997}-\dfrac{1}{1996}-\dfrac{1}{1995}\ne0\) nên \(x+1999=0\Leftrightarrow x=-1999\)
c) \(\dfrac{201-x}{99}+\dfrac{203-x}{97}+\dfrac{205-x}{95}+3=0\)
\(\Rightarrow\dfrac{201-x}{99}+1+\dfrac{203-x}{97}+1+\dfrac{205-x}{95}+1=0\)
\(\Rightarrow\dfrac{300-x}{99}+\dfrac{300-x}{97}+\dfrac{300-x}{95}=0\)
\(\Rightarrow\left(300-x\right)\left(\dfrac{1}{99}+\dfrac{1}{97}+\dfrac{1}{95}\right)=0\)
Vì \(\dfrac{1}{99}+\dfrac{1}{97}+\dfrac{1}{95}\ne0\) nên \(300-x=0\Leftrightarrow x=300\)
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) \(\dfrac{6\cdot9-2\cdot17}{63\cdot3-119}\)
\(=\dfrac{2\left(3\cdot9-17\right)}{7\cdot\left(3\cdot9-17\right)}\)
\(=\dfrac{2}{7}\)
\(\dfrac{x+1}{1998}\)+ \(\dfrac{x+2}{1997}\)=\(\dfrac{x+3}{1996}\)+\(\dfrac{x+4}{1995}\)
=>(x+1/1998+1)+(x+2/1997+1)=(x+3/1996+1)+(x+4/1995+1)
=>x+1999=0
=>x=-1999
Chứng tỏ:
\(1-\dfrac{1}{2}+\dfrac{1}{3}-\dfrac{1}{4}+...+\dfrac{1}{1995}-\dfrac{1}{1996}=\dfrac{1}{996}+\dfrac{1}{997}+...+\dfrac{1}{1990}\)
Giúp Mình vs
Cho \(\frac{1}{a}+\frac{1}{b}+\frac{1}{c}=\frac{1}{a+b+c}\)Chứng minh rằng \(\frac{1}{a^{1995}+b^{1995}+c^{1995}}=\frac{1}{a^{1995}+b^{1995}+c^{1995}}\)