Question

已知4x-3y=6z 2x+4y=14z 求2xy/x^+y^

Answer 1

4x-3y=6z

28x-21y=42z

2x+4y=14z

6x+12y=42z

28x-21y=6x+12y

28x-6x=12y+21y

22x=33y

2x=3y

x/y=3/2

2xy/(x^2+y^2)分子分母同时除以y^2

=(2xy/y^2)/(x^2/y^2+y^2/y^2)

=(2x/y)/(x^2/y^2+1)

=(2*3/2)/[(3/2)^2+1]

=3/(9/4+1)

=3/(13/4)

=3*4/13

=12/13