(x + 3y - 5z) - (x - 3y + 4z)
Remember, subtracting a quantity N is the same as adding -N = -1*N.
In this case:
(x + 3y - 5z) - (x - 3y + 4z)
= (x + 3y - 5z) + (-1)(x - 3y + 4z)
= (x + 3y - 5z) + (-x + 3y - 4z)
= 6y - 9z
(x + 3y - 5z) - (x - 3y + 4z)
Remember, subtracting a quantity N is the same as adding -N = -1*N.
In this case:
(x + 3y - 5z) - (x - 3y + 4z)
= (x + 3y - 5z) + (-1)(x - 3y + 4z)
= (x + 3y - 5z) + (-x + 3y - 4z)
= 6y - 9z