Bài 1: tìm x a) 7/(x+3)(x+10)+11/(x+10)(x+21)+13/(x+2)(x+34)= x/(x+3)(x+34) b) x/2008-1/10-1/15-1/21-….-1/120= 5/8

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1. 7/(x+3)(x+10)+11/(x+10)(x+21)+13/(x+2)(x+34)= x/(x+2)(x+34)( chắc bạn sai cái cuối)

   = 1/( x+ 3) – 1/( x+10) + 1/(x+ 10) – 1/( x+ 21) = x/(x+2)(x+34) – 13/ ( x+ 2). ( x+ 34)

   ⇔ 1/( x+ 3)- 1/(x+ 21) = x- 13/( x+ 2). ( x+ 34)

   Thấy hơi sai đề chút

   ⇔ x+ 21- x- 3/ (x+3). ( x+ 21)= x- 13/( x+ 2). ( x+ 34)

   ⇔ 18/ ( x+ 3). ( x+ 21)= x- 13/( x+ 2). ( x+ 34)

   Sai đề rồi bạn ơi

   x/2008-1/10-1/15-1/21-….-1/120= 5/8

   ⇔ x/2008 – ( 1/10+ 1/15+….+ 1/120)= 5/8

   Đặt B= 1/10+ 1/15+ 1/120

   B: 2= 1/20+ 1/30+…+ 1/240

   B: 2= 1/4.5+ 1/5.6+…+ 1/15. 16

   B: 2= 1/4- 1/5+ 1/5- 1/6+…+ 1/15- 1/16

   B: 2= 1/4- 1/16

   B: 2= 3/16

   B= 3/16 . 2

   B= 3/8

   ⇒ x/2008- 3/8= 5/8

   ⇒ x/ 2008= 5/8+ 3/8

   x/2008= 1

   ⇒ x= 2008

   Vậy x= 2008

   Chúc bạn học tốt!

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