Toán Lớp 6: Bài11 : Tìm x, biết. a. 2(x – 5) – 3(x + 7) = 14 b. 5(x – 6) – 2(x + 3) = 12 c. 3(x – 4) – (8 – x) = 12 d. -7(3x – 5)

Question

Toán Lớp 6:  Bài11 : Tìm x, biết. a.      2(x – 5) – 3(x + 7) = 14 b.     5(x – 6) – 2(x + 3) = 12 c.      3(x – 4) – (8 – x) = 12 d.     -7(3x – 5) + 2(7x – 14) = 28 e.      5(3 – 2x) + 5(x – 4) = 6 – 4x f.       -5(2 – x) + 4(x – 3)  = 10x – 15

tuyethutanhthu · Answer

Giải đáp:     a) x = - 45   b) x = 16   c) x = 8   d) x = - 3    e) x = - 11    f) x = - 7     Lời giải và giải thích chi tiết:      B&agrave;i 11 :     a) 2 . ( x - 5 ) - 3 . ( x + 7 ) = 14     => 2x - 10 - 3x - 21 = 14     => 2x - 3x = 14 + 21 + 10     => - x = 45     => x = - 45     Vậy x = - 45     b) 5 . ( x - 6 ) - 2 . ( x + 3 ) = 12     => 5x - 30 - 2x - 6 = 12     => ( 5x - 2x ) - ( 30 + 6 ) = 12     => 3x = 12 + 36     => 3x = 48     => x = 48/3 = 16     Vậy x = 16     c) 3 . ( x - 4 ) - ( 8 - x ) = 12     => 3x - 12 - 8 + x = 12     => 3x + x = 12 + 12 + 8     => 4x = 24 + 8     => 4x = 32     => x = 32/4 = 8     Vậy x = 8     d) - 7 . ( 3x - 5 ) + 2 . ( 7x - 14 ) = 28     => - 21x + 35 + 14x - 28 = 28     => - 21x + 14x = 28 + 28 - 35     => - 7x = 21     => x = 21/(-7) = - 3     Vậy x = - 3     e) 5 . ( 3 - 2x ) + 5 . ( x - 4 ) = 6 - 4x     => 15 - 10x + 5x - 20 = 6 - 4x     => - 10x + 5x + 4x = 6 - 15 + 20     => - x = 11     => x = - 11     Vậy x = - 11     f) - 5 . ( 2 - x ) + 4 . ( x - 3 ) = 10x - 15     => - 10 + 5x + 4x - 12 = 10x - 15     => - 10 - 12 + 15 = 10x - 5x - 4x      => - 7 = x     Vậy x = - 7

catlantuong · Answer

Đ á p án: a) 2. ( x-5) -3. (x+7)= 14 <=> 2x-10 -3x-21=14 <=> -x -31=14 <=> x=-31-14 <=> x=-45 b) 5(x-6)-2(x+3)=12 <=>5x-30-2x-6=12 <=>3x-36=12 <=>3x=48 <=>x=16 c) 5(x-6)-2(x+3)=12 <=>5x-30-2x-6=12 <=>3x-36=12 <=>3x=48 <=>x=16 d) ⇔-7(3x – 5) + 2(7x – 14) = 28 ⇔-21x+35+14x-28=28 ⇔-21x+14x+35-56=0 ⇔-21x+14x-21=0 ⇔-7x-21=0 ⇔-7(x+3)=0 ⇔x+3=0 ⇔x=-3 e. 5(3 – 2x) + 5(x – 4) = 6 – 4x ⇒15-10x+5x-20=6-4x ⇒ 15-10x+5x-20-6+4x=0 ⇒ -11-x=0 ⇒ x=-11 F.5(2 – x) + 4(x – 3) = 10x – 15 <=> -10 +5x +4x -12 = 10x-15 <=> 5x+4x-10x= -15 +10 +12 <=> -x=7 <=> x=-7 #nocopy Cho mik ctlhn với