Đáp án:
Giải thích các bước giải:
$A=\left(x+5\right)\left(x-3\right)-3x\left(x-2\right)$
$=x^2+2x-15-3x\left(x-2\right)$
$=x^2+2x-15-3x^2+6x$
$=-2x^2+8x-15$
`=>A(2)=-2(3)^2 + 8*3 -15=-9`
$\\$
$B=\left(5x+1\right)\left(1-2x\right)-\left(x-2\right)\left(2x-3\right)$
$=-10x^2+3x+1-\left(x-2\right)\left(2x-3\right)$
$=-10x^2+3x+1-2x^2+7x-6$
$=-12x^2+10x-5$
`B(1)=-12 + 10 -5 =-7`
`B(-1)=-12 - 10 -5 = -27`
$\\$
$C=\left(2x+1\right)\left(2y-1\right)+4x\left(2-y\right)$
$=4xy-2x+2y-1+4x\left(2-y\right)$
$=4xy-2x+2y-1+8x-4xy$
$=6x+2y-1$
`=> C(x;y)= 6*2 - 2 -1=9`
