Toán Lớp 8: Bài 2: Tìm x biết
a) (x – 1)(2 – x) + (x – 3)^2 = 4 – 2x
b) (x + 1)(x + 2)(x – 1) – (x – 2)^3 – x^2 = 7x^2 – 2x + 1
giúp em 1 bài này với ạ em cần gấp lắm
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Toán Lớp 8: Bài 2: Tìm x biết
a) (x – 1)(2 – x) + (x – 3)^2 = 4 – 2x
b) (x + 1)(x + 2)(x – 1) – (x – 2)^3 – x^2 = 7x^2 – 2x + 1
giúp em 1 bài này với ạ em cần gấp lắm
Comments ( 2 )
x(2-x)-1(2-x)+(x-3)(x-3)=4-2x
2x-x²-2+x+x(x-3)-3(x-3)=4-2x
2x-x²-2+x+x²-3x-3x+9=4-2x
(2x+x-3x-3x)+(-x²+x²)+(-2+9)=4-2x
-3x+7=4-2x
-3x+7+2x=4
(-3x+2x)+7=4
-x=4-7
-x=-3
=>x=3
b)(x+1)(x+2)(x-1)-(x-2)³-x²=7x²-2x+1
x(x+2)(x-1)+1(x+2)(x-1)-(x-2)(x-2)(x-2)-x²=7x²-2x+1
x(x²-x+2x-2)+1(x²-x+2x-2)-x(x-2)(x-2)+2(x-2)(x-2)-x²=7x²-2x+1
x³-x²+2x²-2x+x²-x+2x-2-x(x²-2x-2x+4)+2(x²-2x-2x+4)-x²=7x²-2x+1
x³-x²+2x²-2x+x²-x+2x-2-x³+2x²+2x²-4x+2x²-4x-4x+8-x²=7x²-2x+1
(x³-x³)+(-x²+2x²+x²+2x²+2x²+2x²-x²)+(-2x-x+2x-4x-4x-4x)+(-2+8)=7x²-2x+1
7x²-13x+6=7x²-2x+1
(7x²-7x²)-(13x-2x)=1-6
-11x=-5
x=$\frac{5}{11}$
x(2 – x) – 1(2 – x) + (x – 3)(x – 3) = 4 – 2x
2x – x² – 2 + x + x(x – 3) – 3(x – 3) = 4 -2x
2x – x² – 2 + x + x² – 3x – 3x + 9 = 4 – 2x
(2x + x – 3x – 3x) + (-x² + x²) + (-2 + 9) = 4 – 2x
-3x + 7 = 4 – 2x
-3x + 7 + 2x = 4
(-3x + 2x) + 7 = 4
-x = 4 – 7
-x = -3
⇒ x = 3
b) (x + 1)(x + 2)(x – 1) – (x – 2)³ – x² = 7x² – 2x + 1
x(x + 2)(x – 1) + 1(x + 2)(x – 1) – (x – 2)(x – 2)(x – 2) – x² = 7x² – 2x + 1
x(x² – x + 2 x -2) + 1(x² – x + 2 x -2)-x(x – 2)(x – 2) + 2(x – 2)(x – 2)-x² =7x² – 2x + 1
x³ – x² + 2x² – 2x + x² – x + 2x – 2 – x(x² – 2x – 2x + 4) + 2(x² – 2x – 2x +4) – x² = 7x² – 2x + 1
x³ – x² + 2x²- 2x + x² – x + 2x – 2 – x³ + 2x² + 2x²- 4x + 2x² – 4x – 4x + 8 – x² = 7x²- 2x + 1
(x³ – x³) + (-x² + 2x² + x² + 2x² + 2x² + 2x² – x²) + (-2x – x + 2x – 4x – 4x – 4x) + (-2 + 8) = 7x² – 2x + 1
7x² – 13x + 6 = 7x² – 2x + 1
(7x² – 7x²) – (13x – 2x) = 1 – 6
-11x = -5