Question

Which BEST DESCRIBES 3y + 2x + 18?

A)
3y + 2x + 18 is an equation because values can be substituted for x and y.
B)
3y + 2x + 18 is not an expression because both x and y are variables.
3y + 2x + 18 is an expression because it cannot be solved
D)
3y + 2x + 18 is an equation because there are 3 terms

Answer 1

A)

3y + 2x + 18 is an equation because values can be substituted for x and y.

Answer 2

c

Explanation:

A.

2x – 6y = 18 (1)

x – y = 9 <=> y = x -9 (2)

Substitute (2) in (1) we have:

2x – 6(x - 9) = 18

<=> -4x + 54 = 18

<=> x = 9

=> y = 0

There is only 1 solution => A is wrong

B.

2x – 6y = 18 <=> x = 9 + 3y (1)

x + 3y = 9 (2)

Substitute (1) in (2) we have:

(9+ 3y) + 3y = 9

<=> 3y = 0

<=> y = 0

=> x = 9

There is only 1 solution => B is wrong

C.

2x – 6y = 18 (1)

x – 3y = 9 <=> x = 9+ 3y (2)

Substitute (2) in (1) we have:

2(9+3y) - 6y = 18

<=> 18 + 6y - 6y = 18

<=> 18=18

Yes, this system of equations has an infinite number of solutions

So we choose C