Toán Lớp 8: x^2(x-4)+x+6=0 (x-1)(x+3)-(x-2)^2=5

Question

Toán Lớp 8:  x^2(x-4)+x+6=0 (x-1)(x+3)-(x-2)^2=5

cattien · Answer

+, x^2 (x-4) + x + 6 =0   x^3 - 4x^2 + x + 6=0   x^3 +  x^2 - 5x^2  - 5x + 6x +6=0   x^2 (x+1) -5x(x+1) +6(x+1)=0   (x+1)(x^2 - 5x +6)=0   (x+1)(x^2 -2x-3x + 6)=0   (x+1)[ x(x-2) - 3(x-2)]=0   (x+1)(x-2)(x-3)=0    => ( left[  begin{array}{l}x+1=0  x-2=0  x-3=0 end{array}  right. )    => ( left[  begin{array}{l}x=-1  x=2  x=3 end{array}  right. )    +, (x-1)(x+3) - (x-2)^2 =5   x^2 + 3x - x -3 - (x^2 - 4x + 4) =5   x^2 + 3x - x - 3 - x^2 + 4x -4=5   6x -7=5   6x = 12   => x =2

truongthanhhung · Answer

Giải đáp:       Lời giải và giải thích chi tiết:   a)x^2 . ( x - 4 ) + x + 6 = 0    x^3 - 4x^2 + x + 6 = 0   x^3 + x^2 - 5x^2 - 5x + 6x + 6 =0   x^2 ( x + 1) - 5x(x + 1) + 6(x+1)=0   (x+1) . (x^2 - 5x + 6) = 0   (x+1) . (x-2) . (x-3) =0   TH1: x+1 = 0   => x=-1   TH2: x-2=0   =>x=2   TH3: x-3=0   =>x=3   b)( x - 1 ) . ( x + 3 ) - ( x - 2 )^2 = 5   ( x^2 + 3x - 1x - 3) - (x^2 - 2 . x . 2 + 2^2) = 5    x^2 - x^2 + 3x - 1x + 4x  = 3 + 4 + 5    6x = 12    x = 2