Question

Decide whether Y is a function of X

y=-2x-4

Answer 1

yes.
because as you changes x then y changes. it implies that y depends on x.
so y is the function of x.
for example.
substitute x=1
y=-2-4
y=-6
now substitute x=2
y=-4-4
y=-8

see. as x is changes then so y.

I hope this help you.