Charlie uses the function f(x) = 2x^2 + 5x + 3 to track the temperature of a substance, where x represents the time. When you evaluate f(5) you find that the temperature of the substance is 78°C. What is the domain of the situation of Charlie's quadratic function?

A)
all real numbers

B)
all real numbers less than zero

C)
all real numbers greater than zero

D)
all real integers less than or equal to zero

Question

Charlie uses the function f(x) = 2x^2 + 5x + 3 to track the temperature of a substance, where x represents the time. When you evaluate f(5) you find that the temperature of the substance is 78°C. What is the domain of the situation of Charlie's quadratic function?

A)
	all real numbers

B)
	all real numbers less than zero

C)
	all real numbers greater than zero

D)
	all real integers less than or equal to zero

anonymous · Answer

While algebraically the function is valid for all reals, this problem models time as the independent variable. And since you cannot have "negative time" the function is valid for all reals > 0

anonymous · Answer

because time cant be negative? This one is unique from the others?