A=1+3^1+3^2+...+3^2008

3A=3(1+3^1+3^2+...+3^2008)

3A=3*1+3*3^1+3*3^2+...+3*3^2008

3A=3+3^2+3^3+...+3^2009

3A-A=(3+3^2+3^3+...+3^2009)-(1+3^1+3^2+...+3^2008)

A=(3^2009-1):2

=>2A=(3^2009-1):2

<=>A=3^2009-1

vi 2 so lien tiep hon kem nhau 1 don vi

=>3^2009-1 va 3^2009 la 2 so lien tiep

=>2A va B la 2 so tu nhien lien tiep

= 1/2.(1/1.2 - 1/2.3 + 1/2.3 - 1/3.4 + 1/3.4 - 1/4.5 + 1/4.5 - ........+1/98.99 - 1/99.100 )

=1/2.(1/1.2 - 1/99.100)

=1/2 . 4949/9900

=4949/19800

Vì|x+3|=5

=>x+3=5         hoặc        x+3=-5

        x=5-3                           x=(-5)-3

        x=2                               x=-8

Vậy x=2 hoặc x=-8
 

Có 2 trường hợp :

Th1 : x + 3 = 5

=> x = 5 - 3

=> x = 2

Th2 : x + 3 = -5

=> x = -5 - 3

=> x = -8

Vậy có 2 đáp án là ....................

M=1+1/2.3+1/3.6

M=1+3/2+2

M=5/2+2

M=9/2

\(P\left(x\right)=5+x^3-2x+4x^3+3x^2-10=\left(x^3+4x^3\right)+3x^2+2x-\left(10-5\right)=5x^3+3x^2+2x-5\)

\(Q\left(x\right)=4-5x^3+2x^2-x^3+6x-11x^3-8x=-\left(5x^3+x^3+11x^3\right)+2x^2-\left(8x-6x\right)+4=-17x^3+2x^2-2x+4\)

\(P\left(x\right)-Q\left(x\right)=\left(5x^3+3x^2+2x-5\right)-\left(-17x^3+2x^2-2x+4\right)=5x^3+3x^2+2x-5+17x^3-2x^2+2x-4\)

                             \(=\left(5x^3+17x^3\right)+\left(3x^2-2x^2\right)+\left(2x+2x\right)-\left(5+4\right)=22x^3+x^2+4x-9\)