Câu 5: a, x – ( 18 – x ) = x – 8 b, 1 + 3 + 5 + 7 + 9 + … + 99 + x = 10

2 bình luận về “Câu 5: a, x – ( 18 – x ) = x – 8 b, 1 + 3 + 5 + 7 + 9 + … + 99 + x = 10”

1. a) $x-(18-x)=x-8$

   $⇒ x – 18 + x = x-8$

   $⇒ 2x-x=18-8$

   $⇒ x = 10$

   b) $1+3+5+7+…+99+x=10$

   $⇒(99+1).50:2+x=10$

   $⇒2500+x=10$

   $⇒x=10-2500$

   $⇒x=-2490$

   Trả lời
2. a, x – ( 18 – x ) = x – 8

   ⇔ x – 18 + x = x – 8

   ⇔ x – x + x = 18 – 8

   ⇔ x = 10

   Vậy x = 10

   b, 1 + 3 + 5 + 7 + 9 + … + 99 + x = 10

   Gọi A = 1 + 3 + 5 + 7 + … + 99 + x  = 10

   = $\frac{( 99 + 1 ) . 50 }{2}$ + x = 10

   = 2500 + x = 10

   ⇔ x = 10 – 2500

   ⇔ x = (-2490)

   Vậy x = (-2490)

   #tunganh

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