M(x)= 5x4 _ 4x5 + 6x - 2
N(x)= -3x4 + 4x5 - x - 3
a, tìm x để A(x) > 1; A(x) = 1, A(x)<2
b, tính a(1/5), A( 0) , A(1/5)
mọi người giúp mik vs!! ai nhanh + đúngc = 3tick!!
cảm ơn mọi người nhìu!!
Tìm x , biết :
1/3x4 + 1/4x5 + 1/5x6 +...+ 1/97x 98 + 1/98x99 + x =1
1/3x4 + 1/4x5 + 1/5x6 +...+ 1/97x 98 + 1/98x99 + x =1
=> 1/3-1/4+1/4-1/5+1/5-1/6+....+1/97-1/98 + 1/98-1/99 +x = 1
=> 1/3 - 1/99 +x=1
=> 32/99+x=1
=> x= 1-32/99
=> x = 67/99
(x+1/2x3)+(X+1/3x4)+(X+1/4x5)+(X+1/5x6)=25/3
\(\left(x+\dfrac{1}{2\times3}\right)+\left(x+\dfrac{1}{3\times4}\right)+\left(x+\dfrac{1}{4\times5}\right)+\left(x+\dfrac{1}{5\times6}\right)=\dfrac{25}{3}\)
\(x+\dfrac{1}{2\times3}+x+\dfrac{1}{3\times4}+x+\dfrac{1}{4\times5}+x+\dfrac{1}{5\times6}=\dfrac{25}{3}\)
\(x\times4+\left(\dfrac{1}{2\times3}+\dfrac{1}{3\times4}+\dfrac{1}{4\times5}+\dfrac{1}{5\times6}\right)=\dfrac{25}{3}\)
\(x\times4+\left(\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}\right)=\dfrac{25}{3}\)
\(x\times4+\left(\dfrac{1}{2}-\dfrac{1}{6}\right)=\dfrac{25}{3}\)
\(x\times4+\dfrac{4}{12}=\dfrac{25}{3}\)
\(x\times4=\dfrac{25}{3}-\dfrac{4}{12}\)
\(x\times4=\dfrac{25}{3}-\dfrac{1}{3}\)
\(x\times4=\dfrac{24}{3}\)
\(x\times4=8\)
\(x=8\div4\)
\(x=2\)
:))
Tìm số tự nhiên a biết 1/2x3+1/3x4+1/4x5+......+1/a x(a+1)=49/100
=1/2-1/3+1/3-1/4+.......+1/a-1/a+1=49/100
1/2-1/a+1=49/100
1/a+1 = 1/2-49/100
1/a+1=1/100
a+1=100
a=99
=1/2-1/3+1/3-1/4+.......+1/a-1/a+1=49/100
1/2-1/a+1=49/100
1/a+1 = 1/2-49/100
1/a+1=1/100
a+1=100
a=99
Giúp mình giải bài này!Tìm x!Hai x cuối cùng là dấu x
1/1x2+1/2x3+1/3x4+1/4x5+...+1/x+(x+1)
Tìm x thuộc Z biết:
2/2x3+2/3x4+2/4x5+...+2/x(x+1) = 2008/2010
\(\dfrac{2}{2\cdot3}+\dfrac{2}{3\cdot4}+\dfrac{2}{4\cdot5}+...+\dfrac{2}{x\left(x+1\right)}=\dfrac{2008}{2010}\\ 2\cdot\left(\dfrac{1}{2\cdot3}+\dfrac{1}{3\cdot4}+\dfrac{1}{4\cdot5}+...+\dfrac{1}{x\left(x+1\right)}\right)=\dfrac{2008}{2010}\\ \dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+...+\dfrac{1}{x}-\dfrac{1}{x+1}=\dfrac{2008}{2010}:2\\ \dfrac{1}{2}-\dfrac{1}{x+1}=\dfrac{1004}{2010}\\ \dfrac{1}{x+1}=\dfrac{1}{2}-\dfrac{1004}{2010}\\ \dfrac{1}{x+1}=\dfrac{1}{2010}\\ \Rightarrow x+1=2010\\ \Rightarrow x=2009\)
\(\dfrac{2}{2.3}+\dfrac{2}{3.4}+\dfrac{2}{4.5}+...+\dfrac{2}{x\left(x+1\right)}=\dfrac{2008}{2010}\)
\(\Rightarrow2\left(\dfrac{1}{2.3}+\dfrac{1}{3.4}+\dfrac{1}{4.5}+...+\dfrac{1}{x\left(x+1\right)}\right)=\dfrac{2008}{2010}\)
\(\Rightarrow\dfrac{1}{2.3}+\dfrac{1}{3.4}+\dfrac{1}{4.5}+...+\dfrac{1}{x\left(x+1\right)}=\dfrac{502}{1005}\)
\(\Rightarrow\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+...+\dfrac{1}{x}-\dfrac{1}{x+1}=\dfrac{502}{1005}\)
\(\Rightarrow\dfrac{1}{2}-\dfrac{1}{x+1}=\dfrac{502}{1005}\)
\(\Rightarrow\dfrac{1}{x+1}=\dfrac{1}{2010}\)
\(\Rightarrow x+1=2010\Rightarrow x=2009\)
Bậc của đa thức Q ( x ) = x 6 + 5 x 4 + 4 x 5 + x 3 - x 6 - 5 x 4 + 6 là
A. 6
B. 5
C. 4
D. 3
Ta có:
Suy ra đa thức Q(x) có bậc là 5
Chọn đáp án B
P = (1-2/2x3)x(1-2/3x4)x(1-2/4x5) . . . x(1-2/99x100)
\(P=\left(1-\frac{2}{2.3}\right).\left(1-\frac{2}{3.4}\right).\left(1-\frac{2}{4.5}\right)...\left(1-\frac{2}{99.100}\right)\)
\(P=\frac{4}{2.3}.\frac{10}{3.4}.\frac{18}{4.5}...\frac{9898}{99.100}\)
\(P=\frac{1.4}{2.3}.\frac{2.5}{3.4}.\frac{3.6}{4.5}...\frac{98.101}{99.100}\)
\(P=\frac{1.2.3...98}{2.3.4...99}.\frac{4.5.6...101}{3.4.5...100}\)
\(P=\frac{1}{99}.\frac{101}{3}=\frac{101}{297}\)
1/3x4+1/4x5+1/5x6+...+1/11x12=x?
Bài nào khó lắm thì mới hỏi thôi chứ bài này dễ mà bạn tự vận động não đi
\(\dfrac{1}{3\cdot4}+\dfrac{1}{4\cdot5}+...+\dfrac{1}{11\cdot12}=x\)
\(\Leftrightarrow x=\dfrac{1}{3}-\dfrac{1}{12}=\dfrac{4}{12}-\dfrac{1}{12}=\dfrac{1}{4}\)
dễ lắm ko cần hỏi đâu ,tự vận động não đi
B = 1/2x3 + 1/3x4 + 1/4x5 * ... x + 1/ 2022x2023
\(B=\dfrac{1}{2.3}+\dfrac{1}{3.4}+\dfrac{1}{4.5}+...+\dfrac{1}{2022.2023}\)
\(B=\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+...+\dfrac{1}{2022}-\dfrac{1}{2023}\)
\(B=\dfrac{1}{2}-\dfrac{1}{2023}=\dfrac{2021}{4046}\)
1/3x4 + 1/4x5 + 1/5x6 + ... + 1/20x21 = x/14
\(\dfrac{1}{3\times4}+\dfrac{1}{4\times5}+\dfrac{1}{5\times6}+...+\dfrac{1}{20\times21}=\dfrac{x}{14}\)
\(\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}+...+\dfrac{1}{20}-\dfrac{1}{21}=\dfrac{x}{14}\)
\(\dfrac{1}{3}-\dfrac{1}{21}=\dfrac{x}{14}\)
\(\dfrac{7}{21}-\dfrac{1}{21}=\dfrac{x}{14}\)
\(\dfrac{6}{21}=\dfrac{x}{14}\)
\(\Rightarrow x.21=6.14\)
\(x.21=84\)
\(x=84:21\)
\(x=4\)
Vậy x = 4
1/3x4 + 1/4x5 + 1/5x6 + .. + 1/20x21 = x/14
1/3 - 1/4 + 1/4 - 1/5 + 1/5 - 1/6 + .. + 1/20 - 1/21 = x/14
1/3 - 1/21 = x/14
7/21 - 1/21 = x/14
6/21 = x/14
x . 21 = 6 x 14
x x 21 = 84
x = 84 : 21
x = 4
1/(3×4) + 1/(4×5) + 1/(5×6) + ... + 1/(20×21) = x/14
1/3 - 1/4 + 1/4 - 1/5 + 1/5 - 1/6 + ... + 1/20 - 1/21 = x/14
1/3 - 1/21 = x/14
2/7 = x/14
x = 14 × 2/7
x = 4