Toán Lớp 8: bài 3 tìm x biết
a) 10.(x-3) +11 =3x – 1
b) x.(x+4)-5.(3-2x)=(x-2).(2x+2)
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Toán Lớp 8: bài 3 tìm x biết
a) 10.(x-3) +11 =3x – 1
b) x.(x+4)-5.(3-2x)=(x-2).(2x+2)
mn giúp em vs ạ em đang cần gấp
Comments ( 2 )
10.(x-3) +11 =3x – 1
<=>10x-10.3+11=3x-1
<=>10x-30+11-3x+1=0
<=>(10x-3x)+(-30+11+1)=0
<=>7x-18=0
<=>7x=18
<=>x=18/7
Vậy x=18/7
b)
x.(x+4)-5.(3-2x)=(x-2)(2x+2)
<=>x^2+4x-15+10x=2x^2+2x-4x-4
<=>x^2+14x-15=2x^2-2x-4
<=>x^2+14x-15-2x^2+2x+4=0
<=>(x^2-2x^2)+(14x+2x)+(-15+4)=0
<=>-x^2+16x-11=0
<=>-(x^2-16x+11)=0
<=>x^2-16x+11=0
<=>x^2-2.x.8+64-53=0
<=>(x-8)^2=53
<=>[(x-8=sqrt{53}),(x-8=-sqrt{53}):}
<=>[(x=sqrt{53}+8),(x=-sqrt{53}+8):}
Vậy x=8+-sqrt{53}