# I know I'm overthinking

• September 19th 2012, 07:15 PM
franios
I know I'm overthinking
Give a formula for a function with the indicated domain and range:
a) domain all real numbers, range all real numbers
b) domain: the set of integers, range: the set of integers >=2
c) domain:all real numbers, range: the set of reals >=k, where k is a given constant
d) domain: all real numbers, range: {y:a<=y<=b}
e)domain: {x is and element of all real numbers: x>2}, range:{y is an element of all real numbers: y>1}
• September 19th 2012, 08:03 PM
Vlasev
Re: I know I'm overthinking
How are you over-thinking it? I'll give you some hints. In general, it's better to try a simple solution for each of these than a complicated one.

For a) think really simple.
For b) write down the integers from -3 to 3 and the integers from 2 to 8 and try to get a function from the first to the second in an easy, systematic way by drawing arrows.
For c) you can think about functions that go down and then up.
For d) you can think about functions that go up and down but seems to bounce between two values (then you can scale and translate to get them between a and b)
For e) maybe you can think about functions that go bad at 2 and functions that don't exist for x<2, and maybe combine them.
• September 20th 2012, 09:28 AM
franios
Re: I know I'm overthinking
a)y=x
b)y=x+5
is that right?
• September 20th 2012, 09:29 AM
franios
Re: I know I'm overthinking
what do you ean about fractions that go up then down?
• September 20th 2012, 09:30 AM
franios
Re: I know I'm overthinking
• September 20th 2012, 10:16 AM
MarkFL
Re: I know I'm overthinking
Quote:

Originally Posted by franios
what do you ean about fractions that go up then down?

Think of a simple sinusoid:

$f(x)=A\sin(x)+B$

Since $-1\le\sin(x)\le1$ set:

$-A+B=a$

$A+B=b$

Now solve this system for A and B in terms of a and b.