Question

已知m(m-3)-(m的2次方-3n)=9,求2分之m的2次方+n的2次方-mn的值

Answer 1

m(m-3)-(m的2次方-3n)=9
m^2-3m-m^2+3n=9
-3m+3n=9
m-n=9÷(-3)=-3

2分之m的2次方+n的2次方-mn
=1/2×(m-n)^2
=1/2×9
=4.5

Answer 2

即 m²-3m-m²+3n=9
-3m+3n=9
m-n=-3

原式=(m²+n²-2mn)/2
=(m-n)²/2
=(-3)²/2
=9/2