Which equation represents a linear function?

y = 9 - X

y = x2 + 1

o

y=x² + 5

D)

y = [xl - 9

Step-by-step explanation:

y = 9 - X is a linear function; x is to the first power.

y = x2 + 1 does NOT represent a linear function; it's a quadratic function.

o

y=x² + 5 does NOT represent a linear function; it's a quadratic function.

D)

y = [xl - 9 does NOT represent a linear function; it's an absolute value function. This function has two halves, each of which is a linear function.

But the best answer here is that y = 9 - X is a linear function; x is to the first power.