B=5 phan 1.6+5 phan6.11+5 phan 5x+1(6x+6)=2005 phan 2006 BAI VE PHAN SO NHA

Đáp án:

Giải thích các bước giải:

 $\dfrac{5}{1.6}$$+$$\dfrac{5}{6.11}$$+$$…$$+$$\dfrac{5}{(5x+1)(5x+6)}$$=$$\dfrac{2005}{2006}$

$ $

$⇒1-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{11}+…+\dfrac{1}{5x+1}-\dfrac{1}{5x+6}=\dfrac{2005}{2006}$

$ $

$⇒1-\dfrac{1}{5x+6}=\dfrac{2005}{2006}$

$ $

$⇒\dfrac{1}{5x+6}=\dfrac{1}{2006}$

$ $

$⇒5x+6=2006$

$⇒5x=2000$

$⇒x=400$