a)
A= ( 5- x ). (x + 5) - 2.( x - 1). ( x - 3) - 3.( x - 2)2
= 25 - x2 - 2(x2- 3x - x + 3) - 3(x2 - 4x + 4)
= 25 - x2 - 2x2 + 6x + 2x - 6 - 3x2 + 12x - 12
= 7 - 6x2 + 20x
câu b kết quả là:
-14x - 27 +2x2
a) \(A=\left(5-x\right)\left(x+5\right)-2\left(x-1\right)\left(x-3\right)-3\left(x-2\right)^2\)
\(=\left(5-x\right)\left(5+x\right)-\left(2x-2\right)\left(x-3\right)-3\left(x^2-2.2x+2^2\right)\)
\(=\left(5^2-x^2\right)-\left[2x\left(x-3\right)-2\left(x-3\right)\right]-3\left(x^2-4x+4\right)\)
\(=25-x^2-\left[\left(2x^2-6x\right)-\left(2x-6\right)\right]-3x^2+12x-12\)
\(=25-x^2-\left(2x^2-6x-2x+6\right)-3x^2+12x-12\)
\(=25-x^2-2x^2+6x+2x-6-3x^2+12x-12\)
\(=7+20x-6x^2\)
b/ \(B=\left(3-2x\right)\left(x-2\right)+\left(2x-5\right)^2-\left(x-4\right)\)
\(=3\left(x-2\right)-2x\left(x-2\right)+\left[\left(2x\right)^2-2.2x.5+5^2\right]-x+4\)
\(=3x-6-2x^2+4x+4x^2-20x+25-x+4\)
\(=23-14x+2x^2\)
c/ \(C=\left(x-4\right)\left(x-2\right)-3\left(x-2\right)\left(3-2x\right)-\left(2x+1\right)^2\)
\(=x\left(x-2\right)-4\left(x-2\right)-\left(3x-6\right)\left(3-2x\right)-\left[\left(2x\right)^2+2.2x.1+1^2\right]\)
\(=x^2-2x-4x+8-\left[3x\left(3-2x\right)-6\left(3-2x\right)\right]-4x^2-4x-1\)
\(=x^2-2x-4x+8-\left(9x-6x^2-18+12x\right)-4x^2-4x-1\)
\(=x^2-2x-4x+8-9x+6x^2+18-12x-4x^2-4x-1\)
\(=25-31x+3x^2\)
d/ \(D=2\left(x-1\right)^2-3\left(x-1\right)\left(x+2\right)-\left(2x+1\right)^2\)
\(=2.\left(x^2-2x+1\right)-\left(3x-3\right)\left(x+2\right)-\left[\left(2x\right)^2+2.2x+1\right]\)
\(=2x^2-4x+2-\left[3x\left(x+2\right)-3\left(x+2\right)\right]-\left(4x^2+4x+1\right)\)
\(=2x^2-4x+2-\left(3x^2+6x-3x-6\right)-\left(4x^2+4x+1\right)\)
\(=2x^2-4x+2-3x^2-6x+3x+6-4x^2-4x-1\)
\(=7-11x-5x^2\)
P/s: Ko chắc ạ!