Identify the linear equation. a. y = lxl + 5 b. y = 1/2x + 3 c. y =x^2 - 4 d. y = 3/4x^2

answer is b.
c and d are quadratics 

!x! is the absolute value of x, that's what that means..in simple terms, regardless of whether x is positive or negative the value of x will be positive.

Linear equations must be x to the power of 1, so the answer is B, 
 but more knowledge:
C. is a quadratic, i.e. to the power of 2
D. is an exponential i.e. to the power of n, (in this case n equals x). .