Question

求满足方程组2x-y-4m=0 14x-3y=20 中的y值是x值的3倍的m的值,并求xy/x+y的值

Answer 1

y=3x

代入14x-3y=20

14x-9x=20

5x=20

x=4,y=3x=12

代入2x-y-4m=0

8-12=4m

m=-1

xy/(x+y)

=4*12/(4+12)

=3