Bài 1:

Cái này bihf thường:

a.A=

a)P=2(1-5x)(4+5x)+(5x+4)²

=5x-1-50x²-30x+8+25x²+40x+16

=(-50x²+25x²)+(5x-30x+40x)+8+16-1

=-25x²+15x+23

b)Q=(x-y)³+(y+x)³+(y-x)³-3xy(x+y)

=(x+y)³-3xy(x+y)

=x³+y³

1, Thay x = 1/3 ; y = -1/5 ta được 

\(=\dfrac{3.1}{9}-5\left(-\dfrac{1}{5}\right)+1=\dfrac{1}{3}+2=\dfrac{7}{3}\)

2, Thay x = -2 ; y = -1/2 ta được 

\(=5.4\left(-\dfrac{1}{2}\right)+3\left(-2\right)\left(-\dfrac{1}{2}\right)-\dfrac{2\left(-2\right).1}{4}\)

\(=-10+3+1=-6\)

a) P= (5x-1)+2(1-5x)(4+5x)+(5x+4)²

P = (5x-1)² + 2(1 - 5x)(4 + 5x)+ (5x + 4)² - (5x - 1)²

P = (5x - 1 + 5x + 4)² - (5x - 1)²

P = (5x - 1 + 5x + 4 - 5x + 1) (5x - 1 + 5x + 4 + 5x - 1)

b) làm tương tự nhé!! kết quả: Q = x³ + y³

t i c k nha!! 5364574674675678568585785789769647568585

a)\(P=\left(5x-1\right)+2\left(1-5x\right)\left(4+5x\right)+\left(5x+4\right)\)

   \(P=5x-1+5x+4+\left(2-10x\right)\left(4+5x\right)\)

   \(P=10x+3+8+10x-40x-50x^2\)

    \(P=-20x+11-50x^2\)

b)\(Q=\left(x-y\right)^3+\left(y+x\right)^3+\left(y-x\right)^3-3xy\left(x+y\right)\)

   \(Q=x^3-3x^2y+3xy^2-y^3+y^3+3y^2x+3yx^2+x^3+y^3-3y^2x+3yx^2-x^3-3x^2y+3xy^2\)

   \(Q=x^3+y^3\)

a) P = (5x - 1) + [(-2).(-1).(1-5x).(4+5x)] + (5x+4)^2 
= (5x - 1).[(-1)-2.(-1).(4+5x)] + (25x^2+40x+16) 
= [(5x - 1).(10x + 7)] + (25x^2+40x+16) 
= 50x^2 +35x - 10x - 7 + 25x^2+40x+16 
= 75x^2 + 65x -9 
b) Q = (x-y)^3 + (x+y)^3 + (y-x)^3 - [3xy(x+y)] 
Xét (x-y)^3 = x^3 - 3x^2y + 3xy^2 - y^3  = x^3 + 3x^2y + 3xy^2 + y^3  = y^3 - 3xy^2 + 3x^2y - x^3 
Do đó Q = (2x^3 + 6xy^2) + (y^3 - 3xy^2 + 3x^2y - x^3) - [3xy(x+y)] 
= (x^3 + 3xy^2 + 3x^2y + y^3) - 3x^2y - 3xy^2 
= x^3 + y^3

 a, P=(5x-1)+2(1-5x)(4+5x)+(5x+4)

=5x-1+2.(4-15x-5x²)+5x+4

=5x-1+8-30x-10x²+5x+4

=-10x²-20x+11

  b,Q=(x-y)^3 +(y+x)^3+ (y-x)^3 -3xy(x+y)

=x³-3x²y+3xy²-y³+y³+3x²y+3xy²+x³+y³-3y²x+3yx²-x³-3x²y-3xy²

=x³+y³

P=(5x-1).(1+4+5x)+(4+5x)(1-5x+1)

= (5x-1)(5x+5)+(4+5x)(2-5x)

=25x²+20x-5+8-25x²-10x

=10x+3

Q=x³-3x²y+3xy²-y³+x³+3x²y+3xy²+y³+y³-3y²x+3yx²-x³-3xy²-3x²y

=x³+y+3xy(x+y)=(x+y)³