Toán Lớp 8: Bai 5: Tim x, biet:
1. x(x-1)+x(x+2)=2x^2
3. (x-1)(x+1)-2x(x+2)=x(3-x)
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Toán Lớp 8: Bai 5: Tim x, biet:
1. x(x-1)+x(x+2)=2x^2
3. (x-1)(x+1)-2x(x+2)=x(3-x)
Comments ( 2 )
1.
x(x-1)+x(x+2)=2x^2
⇔x^2-x+x^2+2x=2x^2
⇔(x^2+x^2-2x^2)-(x-2x)=0
⇔x=0
Vậy x=0
3.
(x-1)(x+1)-2x(x+2)=x(3-x)
⇔x^2-1-2x^2-4x=3x-x^2
⇔x^2-2x^2+x^2-4x-3x=1
⇔-7x=1
⇔x=-1/7
Vậy x=-1/7
Áp dụng HĐT : a^2-b^2=(a+b)(a-b)
Giải đáp:
1, x = 0
3, x = -1/7
Lời giải và giải thích chi tiết:
Bài 5:
1, x(x – 1) + x(x + 2) = 2x^2
<=> x^2 – x + x^2 + 2x = 2x^2
<=> 2x^2 + x = 2x^2
<=> 2x^2 + x – 2x^2 = 0
<=> x = 0
Vậy x = 0
3, (x – 1)(x + 1) – 2x(x + 2) = x(3 – x)
<=> x^2 – 1 – 2x^2 – 4x = 3x – x^2
<=> -x^2 – 4x – 1 = 3x – x^2
<=> -x^2 – 4x – 1 – 3x + x^2 = 0
<=> -7x – 1 = 0
<=> -7x = 1
<=> x = -1/7
Vậy x= -1/7