Question

It is known that `x + y =15` and `y + z = 10`, simplify `6(x^2+y^2+z^2) -15xy + 20yz – 13zx`?

Answer 1

`0`

Explanation:

Solving

`{(x+y=15),(y+z=10):}`

we have

`y = 15-x` and `z=x-5`

Substituting into `6(x^2+y^2+z^2) -15xy + 20yz – 13zx` we obtain

`6(x^2+y^2+z^2) -15xy + 20yz – 13zx=0`