If ab + bc + ca=0 , then the value of 1/a^2-bc + 1/b^2-ca + 1/c^2-ab=?

If ab + bc + ca=0 , then the value of 1/a^2-bc + 1/b^2-ca + 1/c^2-ab=?

 ab + bc + ca=0  …………….(1)

We have ,

Using eqn (1) , we can write

But we know ,

bc + ac + ab = 0

hence,  = 0 ans