From the sum of `2y^2+3yz, -y^2-yz-z^2 and yz+2z^2,` subtract the sum of `3y^2-z^2 and -y^2+yz+z^2`

Explanation

finding sum

`2y^2 + 3yz + (-y^2 - yz - z^2) + (yz + 2z^2)`

`= y^2 + 3yz + z^2`eqn(1)

finding sum of other terms

`3y^2 - z^2 + (-y^2 + z^2 + yz)`

`= 2y^2 + yz` eqn(2)

subtracting 1 & 2

`= y^2+ 3yz + z^2-(2y^2+yz)`

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