Toán Lớp 6: tìm x biết, a, 45-12x=-15 b,(xmũ2-16).(x+3)=0 c,100:(2.(x+5)-12)=-5 d,(x+5)-12)=-5

Question

Toán Lớp 6:  tìm x biết,      a, 45-12x=-15   b,(xmũ2-16).(x+3)=0                         c,100:(2.(x+5)-12)=-5    d,(x+5)-12)=-5

truonganhthi · Answer

${ a) 45 - 12x = -15 }$   ${ &rArr; 12x = 45 + 15 }$   ${ &rArr; 12x = 60 }$   ${ &rArr; x = 5 }$   Vậy ${ x = 5 }$   ${ b) (x^2 - 16).(x + 3) = 0 }$   ${ &rArr;  left[ begin{matrix} x^2 - 16 = 0   x + 3 = 0 end{matrix} right. }$   ${ &rArr;  left[ begin{matrix} x = &plusmn; 4   x = -3 end{matrix} right. }$   Vậy ${ x = 4; x = -4 }$ v&agrave; ${ x = -3 }$   ${ c) 100 : (2. (x + 5) - 12) = -5 }$   ${ &rArr; 2. (x + 5) - 12 = 100 : (-5) }$   ${ &rArr; 2. (x + 5) - 12 = -20 }$   ${ &rArr; 2. (x + 5) = -8 }$   ${ &rArr; x + 5 = -4 }$   ${ &rArr; x = -1 }$   Vậy ${ x = -1 }$   ${ d) (x + 5) - 12 = -5 }$   ${ &rArr; x + 5 = -5 + 12 }$   ${ &rArr; x + 5 = 7 }$   ${ &rArr; x = 2 }$   Vậy ${ x = 2 }$

tuminh25 · Answer

a. 45 - 12x = -15   =>12x = 45 - (-15)   =>12x = 45 + 15 = 60   =>x = 60 : 12   =>x = 5   Vậy x = 5   ________________________   b. (x^2 - 16)(x + 3) = 0   =>$ left[ begin{matrix}x^2 - 16 = 0   x+3=0 end{matrix} right.$   =>$ left[ begin{matrix}x^2 = 0 + 16   x=0 - 3 end{matrix} right.$   =>$ left[ begin{matrix}x^2 = 16   x = -3 end{matrix} right.$   =>$ left[ begin{matrix}x^2 = (+-4)^2   x = -3 end{matrix} right.$   =>$ left[ begin{matrix}x = +-4   x=-3 end{matrix} right.$   Vậy x = +-4 ; x = -3   _________________________   c. 100 : [2 . (x + 5) - 12] = -5   =>[2 . (x + 5) - 12] = 100 : (-5)   =>2 . (x + 5) - 12 = -20   =>2 . (x + 5) = -20 + 12   =>2 . (x + 5) = -8   =>x + 5 = -8 : 2   =>x + 5 = -4   =>x = -4 - 5   =>x = -9   Vậy x = -9   _____________________________   d. [(x + 5) - 12] = -5   =>(x + 5) = -5 + 12   =>x + 5 = 7   =>x = 7 - 5   =>x = 2   Vậy x = 2