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Bài 1:
a) -6x + 3(7 + 2x)
= -6x + 21 + 6x
= (-6x + 6x) + 21
= 21
b) 15y - 5(6x + 3y)
= 15y - 30 - 15y
= (15y - 15y) - 30
= -30
c) x(2x + 1) - x2(x + 2) + (x3 - x + 3)
= 2x2 + x - x3 - 2x2 + x3 - x + 3
= (2x2 - 2x2) + (x - x) + (-x3 + x3) + 3
= 3
d) x(5x - 4)3x2(x - 1) ??? :V
Bài 2:
a) 3x + 2(5 - x) = 0
<=> 3x + 10 - 2x = 0
<=> x + 10 = 0
<=> x = -10
=> x = -10
b) 3x2 - 3x(-2 + x) = 36
<=> 3x2 + 2x - 3x2 = 36
<=> 6x = 36
<=> x = 6
=> x = 5
c) 5x(12x + 7) - 3x(20x - 5) = -100
<=> 60x2 + 35x - 60x2 + 15x = -100
<=> 50x = -100
<=> x = -2
=> x = -2
a) 3x(x + 2) + 4x(-2x + 3) + (2x - 3)(3x + 1)
= 3x2 + 6x - 8x2 + 12x + 6x2 + 2x - 9x - 3
= (3x2 - 8x2 + 6x2) + (6x + 12x + 2x - 9x) - 3
= x3 + 11x - 3
b) (x2 + 1)(x2 - x + 2) - (x2 - 1)(x2 + x - 2)
= x4 - x3 + 3x2 - x + 2 - x4 - x3 + 3x2 + x - 2
= (x4 - x4) + (-x3 - x3) + (3x2 + 3x2) + (-x + x) + (2 - 2)
= -2x3 + 6x2
c) (-2x - 3)2 + (3x + 2)2 + (4x + 1)
= 4x2 + 12x + 9 + 9x2 + 12x + 4 + 4x + 1
= (4x2 + 9x2) + (12x + 12x + 4x) + (9 + 4 + 1)
= 13x2 + 28x + 14
a) Ta có : \(A\left(x\right)+B\left(x\right)\)
\(=2x^3+2x-3x^2+1+2x^2+3x^3-x-5\)
\(=\left(2x^3+3x^3\right)+\left(-3x^2+2x^2\right)+\left(2x-x\right)+\left(1-5\right)\)
\(=5x^3-x^2-x-4\)
b) Ta sẽ sắp xếp như sau :
\(A\left(x\right)=2x^3-3x^2+2x+1\)
\(B\left(x\right)=3x^3+2x^2-x-5\)
c) Ta có : \(A\left(x\right)-B\left(x\right)\)
\(=\left(2x^3+2x-3x^2+1\right)-\left(2x^2+3x^3-x-5\right)\)
\(=2x^3+2x-3x^2+1-2x^2-3x^3+x+5\)
\(=\left(2x^3-3x^3\right)+\left(-3x^2-2x^2\right)+\left(2x+x\right)+\left(1+5\right)\)
\(=-x^3-5x^2+3x+6\)
a)
A(x)= x4 - 2x3 + 4x - 1
B(x)=3x4 +x3 -x2 - 3x -2
A(x)+B(x) =4x4 -3x3-x2 +x -3
b/ A(x)= x4 - 2x3 + 4x - 1
B(x)=3x4 +x3 -x2 - 3x -2
A(x)-B(x) =-2x4 -3x3-x2 +7x +1
c/
B(x)=3x4 +x3 -x2 - 3x -2
A(x)= x4 - 2x3 + 4x - 1
B(x)-A(x)=2x4 +3x3 -x2 -7x -1
a) Ta có:
\(x^4-2x^3+4x-1+3x^4+x^3-x^2-3x-2\)
\(\Leftrightarrow4x^4-x^3-x^2-x-3\)
b)
\(x^4-2x^3+4x-1-\left(3x^4+x^3-x^2-3x-2\right)\)
\(\Leftrightarrow x^4-2x^3+4x-1-3x^4-x^3+x^2+3x+2\)
\(\Leftrightarrow-2x^4-3x^3+x^2+7x+1\)
c)
\(3x^4+x^3-x^2-3x-2-\left(x^4-2x^3+4x-1\right)\)
\(\Leftrightarrow3x^4+x^3-x^2-3x-2-x^4+2x^3-4x+1\)
\(\Leftrightarrow2x^4+3x^3-x^2-7x-1\)
a) \(A\left(x\right)+B\left(x\right)=\left(x^3-3x^2+3x-1\right)+\left(x^3+3x^2+3x+1\right)\)
\(=x^3-3x^2+3x-1+x^3+3x^2+3x+1\)
\(=\left(x^3+x^3\right)+\left(-3x^2+3x^2\right)+\left(3x+3x\right)+\left(-1+1\right)\)
\(=2x^3+6x\)
b) \(A\left(x\right)-B\left(x\right)+C\left(x\right)=\left(x^3-3x^2+3x-1\right)-\left(x^3+3x^2+3x+1\right)+\left(2x^2+3x+2\right)\)
\(=x^3-3x^2+3x-1-x^3-3x^2-3x-1-2x^2-3x-2\)
\(=\left(x^3-x^3\right)+\left(-3x^2-3x^2-2x^2\right)+\left(3x-3x-3x\right)+\left(-1-1-2\right)\)
\(=-8x^2-3x-4\)
a, \(A\left(x\right)+B\left(x\right)=2x^3-6x\)
hOK TỐT
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