giải các pt sau : a) 7x+21=0 b)x+5/4-2x-3/3=6x-1/8+2x-1/12 c)x+1/65+x+3/63=x+5/61+x+7/59

0 bình luận về “giải các pt sau : a) 7x+21=0 b)x+5/4-2x-3/3=6x-1/8+2x-1/12 c)x+1/65+x+3/63=x+5/61+x+7/59”

1. $a)$ `7x+21=0`

   `⇔ 7x = -21`

   `⇔ x = -3`

    Vậy `S= {-3}`

   $b)$ `(x+5)/4 – (2x-3)/3= (6x-1)/8 + (2x-1)/12`

   `⇔ [3.(x+5)]/12 – (4.(2x-3))/12 = (3.(6x-1))/24 + [2.(2x-1)]/24`

   `⇔ (3x +15)/12 – (8x -12)/12 = (18x -3)/24 + (4x -2)/24`

   `⇔ (3x +15 -8x +12)/12 = (18x -3 +4x -2)/24`

   `⇔ (-5x +27)/12 = (22x -5)/24`

   `⇒ 24.(-5x +27) = 12.(22x -5)`

   `⇔ -120x +648 = 264x – 60`

   `⇔ -120x -264x = -60 -648`

   `⇔ -384x = -708`

   `⇔ x = 59/32`

     Vậy` S = {59/32}`

   $c)$ `(x+1)/65 + (x+3)/63= (x+5)/61 + (x+7)/59`

   `⇔ (x+1)/65 +1 +(x+3)/63 +1 = 1+ (x+5)/61 +1 +(x+7)/59`

   `⇔ (x +66)/65 + (x +66)/63 = (x +66)/61 + (x +66)/59`

   `⇔ (x +66)/65 + (x +66)/63 – (x +66)/61 – (x +66)/59 = 0`

   `⇔ (x +66).( 1/65 + 1/63 – 1/61 – 1/59)^{(1)} = 0` `[`Vì `(1) ne 0]`

   `⇒ x +66 = 0`

   `⇒ x = -66`

    Vậy `S = {-66}`

   Trả lời