Toán Tìm x : 1/3+1/6+1/10+….+2/x×(x+1)=2005/2007 16/11/2021 By Elliana Tìm x : 1/3+1/6+1/10+….+2/x×(x+1)=2005/2007
1/3+1/6+1/10+….+2/x×(x+1)=2005/2007 ⇔26 +212 +220 +...+2x(x+1) =2005/2007 ⇔22.3 +23.4 +24.5 +...+2x(x+1) =2005/2006 ⇔2.(12.3 +13.4 +14.5 +...+1x(x+1) )=2005/2007 ⇒2.(12 −13 +13 −14 +14 −15 +...+1x −1x+1 )=2005/2007 ⇒2.(12 −1x+1 )=2005/2007 ⇒12 −1x+1 =2005/2007 :2 ⇒12 −1x+1 =2005/4014 ⇒1x+1 =12 −2005/4014 ⇒1x+1 =1/2007 ⇒x+1=1/2007 => x = 2007 – 1 => x = 2006 chúc bn học tốt!!! Trả lời
1/3+1/6+1/10+….+2/x×(x+1)=2005/2007
⇔26 +212 +220 +...+2x(x+1) =2005/2007
⇔22.3 +23.4 +24.5 +...+2x(x+1) =2005/2006
⇔2.(12.3 +13.4 +14.5 +...+1x(x+1) )=2005/2007
⇒2.(12 −13 +13 −14 +14 −15 +...+1x −1x+1 )=2005/2007
⇒2.(12 −1x+1 )=2005/2007
⇒12 −1x+1 =2005/2007 :2
⇒12 −1x+1 =2005/4014
⇒1x+1 =12 −2005/4014
⇒1x+1 =1/2007
⇒x+1=1/2007
=> x = 2007 – 1
=> x = 2006
chúc bn học tốt!!!