Toán Lớp 8: tìm x, bt a,x^2+6x+9=0 b,2x^2+20x+50=0 c,x^2+2x-3=0 d,4x^2+12x+10 vd:a,x^2+14x+49=0 x^2 + 2x.7+7^2=0 (x+7)^2=0 x+7=0 x=-7 b,3

Question

Toán Lớp 8:  tìm x, bt  a,x^2+6x+9=0  b,2x^2+20x+50=0  c,x^2+2x-3=0  d,4x^2+12x+10  vd:a,x^2+14x+49=0  x^2 + 2x.7+7^2=0  (x+7)^2=0  x+7=0  x=-7  b,3x^2+6x-24=0  3.(x^2 +2x-8)=0  x^2+2x-8=0  x^2+2x+1-9=0 x^2+2x.1+12=19 (x+1)^2=9  x+1=3 or c+1=-3  x=3-1 or x=-3-1  x=2 or x=-4

tonhitruc · Answer

Giải đáp:       Lời giải và giải thích chi tiết:    a,x^2+6x+9=0     x^2 +2.x.3 +3^2 = 0     (x+3)^2 =0     x+3=0     x=-3     b,2x^2+20x+50=0     2.x^2 + 2.10x + 2.25 = 0     2(x+10x+25)=0     2(x+2.x.5 +5^2)=0     2(x+5)^2 =0     (x+5)^2 =0     x+5=0     x=-5     c,x^2+2x-3=0     x^2 +3x-x-3=0     (x^2 -x)+(3x-3)=0     x(x-1)+3(x-1)=0     (x+3)(x-1)=0     $ left[ begin{matrix} x+3=0   x-1=0 end{matrix} right.$     $ left[ begin{matrix} x=-3   x=1 end{matrix} right.$     d,4x^2+12x+10=0    4x^2 +12x+9+1=0   (2x)^2 +2.2x.3 +3^2 +1=0   (2x+3)^2 +1=0   (2x+3)^2 = -1   V&ocirc; l&iacute; v&igrave; (2x+3)^2 &ge;0 &forall; x