Question

Bài 1:Rút gọn biểu thức 

a,A=(x-3).(x+7)-(x+5).(x-1)

b,B=(x+8)²-2.(x+8).(x-2)+(x-2)²

c,C=x².(1+2x²)-2x.(x+1).(x²-x+1)+1

d,D=(x-y).(x+y)+(x-y)²+(x+y)²

Answer 1

a)

\(=x^2+7x-3x-21-\left(x^2-x+5x-5\right)\)

\(=x^2+7x-3x-21-x^2+x-5x+5\)

\(=x^2-x^2+7x-3x+x-5x-21+5\)

\(=-16\)

b)

\(=x^2+16x+64-2\left(x^2-2x+8x-16\right)+x^2-4x+4\)

\(=x^2+16x+64-2x^2+4x-16x+32+x^2-4x+4\)

\(=x^2-2x^2+x^2+16x+4x-16x-4x+64+32+4\)

\(=100\)

c)

\(=x^2+2x^4-2x\left(x^3+1\right)+1\)

\(=x^2+2x^4-2x^4-2x+1\)

\(=2x^4-2x^4+x^2-2x+1\)

\(=x^2-2x+1\)

d)

\(=x^2-y^2+x^2-2xy+y^2+x^2+2xy+y^2\)

\(=x^2+x^2+x^2-2xy+2xy-y^2+y^2+y^2\)

\(=3x^2+y^2\)