# Thread: Another function

1. ## Another function

Find the range of each function . For any function that is not one to one , give two distinct values of x which have the same image .

(1) $f(x)=sin x$ , x are real numbers

(2) $g(x)=\sqrt{x}+\sqrt{1+x}$ , $o\geq x \geq1$ ,

(3) $h(x)=In{x}$ , $x>0$

the range for sine function is [-1,1]

but for the rest , i am not really sure .

2. ## Range of function

Hello thereddevils
Originally Posted by thereddevils
Find the range of each function . For any function that is not one to one , give two distinct values of x which have the same image .

(1) $f(x)=sin x$ , x are real numbers

(2) $g(x)=\sqrt{x}+\sqrt{1+x}$ , $o\geq x \geq1$ ,

(3) $h(x)=In{x}$ , $x>0$

the range for sine function is [-1,1]

but for the rest , i am not really sure .
(1) $f$ is not one-to-one; e.g. $f(0) = f(\pi)$

(2) I presume you mean $0\le x\le 1$, in which case, since $g$ is an increasing function for $x \ge 0$, the range is $[1, 1+\sqrt{2}]$; and $g$ is one-to-one.

(3) The function $\text{ln}x$, for $x > 0$, has the whole of $\mathbb{R}$ as its range. And it is also one-to-one.

3. Originally Posted by thereddevils
Find the range of each function . For any function that is not one to one , give two distinct values of x which have the same image .

(1) $f(x)=sin x$ , x are real numbers

(2) $g(x)=\sqrt{x}+\sqrt{1+x}$ , $o\geq x \geq1$ ,

(3) $h(x)=In{x}$ , $x>0$

the range for sine function is [-1,1]

but for the rest , i am not really sure .
(1) You know that sin x is periodic with period $2\pi$. That should give you an easy answer.
(2) This is a little harder because this is one to one. I would show that by arguing that the derivative is always positive and so the function is increasing but I don't know what methods you have available.
(3) I don't recognise "In(x)". Do you mean the natural logarighm? That is ln(x)- "logarithm" starts with a "l" not "I"! If so, same comments as in (2) apply.

4. Originally Posted by Grandad
Hello thereddevils(1) $f$ is not one-to-one; e.g. $f(0) = f(\pi)$

(2) I presume you mean $0\le x\le 1$, in which case, since $g$ is an increasing function for $x \ge 0$, the range is $[1, 1+\sqrt{2}]$; and $g$ is one-to-one.

(3) The function $\text{ln}x$, for $x > 0$, has the whole of $\mathbb{R}$ as its range. And it is also one-to-one.

Thanks once again . For (2) If the function is one to one , does it mean that the function will be one to one ?

5. Originally Posted by HallsofIvy
(1) You know that sin x is periodic with period $2\pi$. That should give you an easy answer.
(2) This is a little harder because this is one to one. I would show that by arguing that the derivative is always positive and so the function is increasing but I don't know what methods you have available.
(3) I don't recognise "In(x)". Do you mean the natural logarighm? That is ln(x)- "logarithm" starts with a "l" not "I"! If so, same comments as in (2) apply.

For (2) , i made a typo , Grandad has corrected it .

For (3) , yes it is a natural log . sorry for that mistake , ln

Thanks for pointing out .

6. Hello thereddevils
Originally Posted by thereddevils
Thanks once again . For (2) If the function is one to one , does it mean that the function will be one to one ?
Sorry, I don't understand!

7. Originally Posted by Grandad
Hello thereddevilsSorry, I don't understand!

Yes, providing it's a strictly increasing function - in other words, it doesn't have any sections where the gradient is zero. This is true of the function $g(x)$.