18. If [tex]x = 2z[/tex] and [tex]y = 3z[/tex], express the following in terms of [tex]z[/tex], and find the value of both expressions when [tex]z = ?[/tex]:

(a) [tex]x + y + z[/tex]

(b) [tex]nx - 3y + 42[/tex]



Answer :

Certainly! Let's tackle each part of the problem methodically.

### Given:
- [tex]\( x = 2 \)[/tex]
- [tex]\( y = 3 \)[/tex]
- [tex]\( z \)[/tex] is a variable

### (a) Express [tex]\( x + y + z \)[/tex] in terms of [tex]\( z \)[/tex]
We begin by substituting the known values of [tex]\( x \)[/tex] and [tex]\( y \)[/tex]:

[tex]\[ x + y + z = 2 + 3 + z \][/tex]

Combining the constants:

[tex]\[ x + y + z = 5 + z \][/tex]

So, the expression in terms of [tex]\( z \)[/tex] is:

[tex]\[ x + y + z = 5 + z \][/tex]

### (b) Express [tex]\( n \cdot x - 3 \cdot y + 42 \)[/tex] in terms of [tex]\( z \)[/tex]

Here, [tex]\( n \)[/tex] is an unspecified variable. We substitute [tex]\( x = 2 \)[/tex] and [tex]\( y = 3 \)[/tex]:

[tex]\[ n \cdot x - 3 \cdot y + 42 = n \cdot 2 - 3 \cdot 3 + 42 \][/tex]

Now, perform the arithmetic:

[tex]\[ n \cdot 2 - 9 + 42 = 2n - 9 + 42 \][/tex]

Combine the constants:

[tex]\[ 2n + 33 \][/tex]

So, the expression in terms of [tex]\( z \)[/tex] (though it does not actually involve [tex]\( z \)[/tex]) is:

[tex]\[ 2n + 33 \][/tex]

### Value of Expressions When [tex]\( z \)[/tex] is Given

Let's compute the values of both expressions for a specific [tex]\( z \)[/tex]. Suppose [tex]\( z = 0 \)[/tex]:

1. For [tex]\( x + y + z \)[/tex]:
[tex]\[ x + y + z = 5 + z = 5 + 0 = 5 \][/tex]
So the value is [tex]\( 5 \)[/tex].

2. For [tex]\( n \cdot x - 3 \cdot y + 42 \)[/tex]:
[tex]\[ 2n + 33 \][/tex]

Since there’s no specified value for [tex]\( n \)[/tex], the value remains an expression in terms of [tex]\( n \)[/tex]:
[tex]\[ 2n + 33 \][/tex]

If we assume [tex]\( n = 1 \)[/tex] for a concrete example:
[tex]\[ 2 \cdot 1 + 33 = 2 + 33 = 35 \][/tex]

So for [tex]\( n = 1 \)[/tex], the value is [tex]\( 35 \)[/tex].

### Conclusion:
- The expression (a) [tex]\( x + y + z \)[/tex] in terms of [tex]\( z \)[/tex] is [tex]\( 5 + z \)[/tex].
- The expression (b) [tex]\( n \cdot x - 3 \cdot y + 42 \)[/tex] is [tex]\( 2n + 33 \)[/tex].
- For [tex]\( z = 0 \)[/tex], [tex]\( x + y + z \)[/tex] evaluates to [tex]\( 5 \)[/tex].
- For [tex]\( n = 1 \)[/tex], [tex]\( 2n + 33 \)[/tex] evaluates to [tex]\( 35 \)[/tex].