已知多项式2xˆ2+my-12与多项式nxˆ2-3y+6的和中不含有x,y,试求mn的值已知,3aˆx1b与ab是同类项,3aˆx2b与aˆ2b是同类项,3aˆx3b与aˆ3b是同类项,...,3aˆxkb与akb是同类项,求1/x1x2+1/x2x3+1/x3x4+...+1/x49x50

2xˆ2+my-12与多项式nxˆ2-3y+6的和中不含有x,y
2xˆ2+my-12+nxˆ2-3y+6
=(n+2)x^2+(m-3)y-6
∴m=3
∴mn=3n
如果题目改为2xˆ2+my-12与多项式nxˆ2-3y+6的和中不含有x^2,y:
2xˆ2+my-12+nxˆ2-3y+6
=(n+2)x^2+(m-3)y-6
∴m=3,n=-2
∴mn=3*(-2)=-6
【问题补充】
3aˆx1b与ab是同类项,∴x1=1
3aˆx2b与aˆ2b是同类项,∴x2=2
3aˆx3b与aˆ3b是同类项,∴x3=3
...,
3aˆxkb与akb是同类项,∴xk=k
1/x1x2+1/x2x3+1/x3x4+...+1/x49x50
=1/(1*2)+1/(2*3)+1/(3*4)+...+(1/(49*50)
=1/1-1/2+1/2-1/3+.-1/49+1/49-1/50
=1-1/50
=49/50