Question

Answer 1

a: \(A=a\left(b+3\right)-b\left(3+b\right)\)

\(=\left(b+3\right)\left(a-b\right)\)

Khi a=2003 và b=1997 thì \(A=\left(1997+3\right)\left(2003-1997\right)=6\cdot2000=12000\)

b: \(B=b^2-8b-c\left(8-b\right)\)

\(=b\left(b-8\right)+c\left(b-8\right)\)

\(=\left(b-8\right)\left(b+c\right)\)

Khi b=108 và c=-8 thì \(B=\left(108-8\right)\left[108+\left(-8\right)\right]\)
\(=100\cdot100\)

=10000

c: \(C=xy\left(x+y\right)-2x-2y\)

\(=xy\left(x+y\right)-2\left(x+y\right)\)

=(x+y)(xy-2)

Khi xy=8 và x+y=7 thì \(C=7\cdot\left(8-2\right)=7\cdot6=42\)