Which of the following is a linear expression?

• A. 4x + 2y - 7
• B. x^2 + 3
• C. xy + 1
• D. 3/x + 2

Answer: (A)

Linear expressions are sums of constants and first powers of the variables, with no products of variables or variable in denominators. They have the form a x + b y + c, where a, b, c are constants. The expression 4x + 2y - 7 fits this form: each variable appears to the first power, there are no cross-terms like xy, and -7 is a constant. The other options fail because x^2 + 3 has x squared, xy + 1 has a product of two variables, and 3/x + 2 involves a reciprocal of x, which is not linear.