A= ax+bx-ay-by (với a+b=-7;x-y=-1)
A = 10a + x + 10b + x - ( 10a + y ) - ( 10b + y )
A = (10a - 10a) + ( 10b - 10b) + 2x - 2y = 2(x-y) = -2
A= x(a+b)-y(a+b)
A= x (-7) -y(-7)
A= (-7) (x-y)
A= (-7) (-1)
A= 7
\(A=ax+bx-ay-by\)
\(=x\left(a+b\right)-y\left(a+b\right)\)
\(=x\left(-7\right)-y\left(-7\right)\)
\(=\left(-7\right)\left(x-y\right)\)
\(=\left(-7\right)\left(-1\right)=7\)