Marrie is logging the number of radioactive isotope she observes every minute. She has determined her function to be f(x) =-4x +120. Based on the situatuion above describe and neccesary restrictions to the domain and range

Question

anonymous · Answer

i guess the domain is minutes, so you would have to restrict it to positive numbers, as, (alas) you cannot go backwards in time

anonymous · Answer

also presumably you cannot have a negative number of isotopes, so the range has to be greater then zero
this means also for the domain you have to solve 
$$-4x+120\geq 0$$

anonymous · Answer

*greater than or equal to zero 
not "greater then zero"

anonymous · Answer

Ok ..uh I dont understand anything lol ..can u break it down for me?

anonymous · Answer

do you know what "domain" means?

anonymous · Answer

the x and y values yess

anonymous · Answer

no that is not what it means
the "domain" means the possible inputs of the function

anonymous · Answer

Oh  :/  eh

anonymous · Answer

@satellite73

agent0smith · Answer

x is time. Time can not be negative, which is why x ≥ 0. Understand?

anonymous · Answer

Yes!

anonymous · Answer

it says to justify your anwer for the restictions

agent0smith · Answer

That's part of the domain, x ≥ 0. Remember DOMAIN is x values, not y values.

The other part of the domain, as satellite said, you can't have a negative number of isotopes. So for f(x) =-4x +120, the $$\large -4x+120\geq 0 $$ which you need to solve.

anonymous · Answer

x = 30

agent0smith · Answer

Not quite correct. There isn't an equals sign here $$\large -4x+120\geq 0$$
So there won't be an equals sign in your answer.

anonymous · Answer

x>30 ..sorry

agent0smith · Answer

Not quite but closer. $$\large -4x+120\geq 0$$ first subtract 120 from both sides $$\large -4x \ge -120$$ now divide both sides by -4. What happens when you divide both sides of an inequality by a negative number?

anonymous · Answer

becomes poitive

agent0smith · Answer

What happens to the sign of the inequality when you divide both sides by a negative?

anonymous · Answer

it flips?

anonymous · Answer

x<30

agent0smith · Answer

Correct. So we had  x ≥ 0 and now we have x =< 30. Which we can combine, since x is greater than or equal to 0, and less than or equal to 30 $$\Large 0 \le x \le 30$$ That's our domain.