we have that
y = 2x + 8
for x=1-----------> y=2*1+8=10
for x=2-----------> y=2*2+8=12
for x=3-----------> y=2*3+8=14
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the equation y = 2x + 8 ----------- > defines y as a function of x, because for each x there is only one value of y.
the answer is
yes, the equation y = 2x + 8 defines y as a function of x