Given:
A=(7xy+5yz−3zx)
B=(4yz+9zx−4y)
C=(−3xz+5x−2xy)
To find the value of A+B+C we write the expressions one below the other with the like terms appearing exactly below like terms as:
7xy+5yz−3zx
4yz+9zx−4y
−2xy −3xz +5x
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5xy+9yz+3xz−4y+5x
Thus, A+B+C=5xy+9yz+3xz+5x−4y.