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avatar+363 

Okay, so I've never eally been clear on how to find domain and range of a function. Could someone explain how to get them then demonstrate on the problem \({4}^{2x}-5\)

 
AdamTaurus  Oct 13, 2017
edited by AdamTaurus  Oct 13, 2017
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3+0 Answers

 #1
avatar+76972 
+1

42x  - 5

 

This is an exponential.......the domain for an exponential is all real numbers  [ note....2x is defined for all real numbers....so.....42x  is, too....because the exponent is just a real number ]

 

The range is trickier.......if it was just    42x  the range would be  (0, infinity)

 

However.......the " - 5 "   part  shifts the graph down by 5 units.....so.....the range now becomes

(-5, infinity)

 

See the graph here :  https://www.desmos.com/calculator/szmhu8kwjm

 

Notice that graph almost touches   y = -5    [ but not quite  !!!]

 

 

cool cool cool

 
CPhill  Oct 13, 2017
 #2
avatar+363 
0

Could you also possibly do the domain and range of -sqrt(2x-6).

 
AdamTaurus  Oct 13, 2017
 #3
avatar+76972 
+2

y  = - √ [ 2x -6]

 

First.....since we can't take the square root of something < 0....then  2x  - 6  must be ≥ 0

 

So

 

2x  - 6 ≥  0

2x ≥ 6

x ≥ 3     and this is the domain  →    [3, infinity )

 

The range is a little tougher

 

The  greatest  value that  y can be is when x = 3......which means that y = 0

Note that all x's greater than 3 produce  a larger and larger square root....but...the " - " out front means that  we gett larger and larger negative square roots......so......the range is actually  

( - infinity, 0 ]

 

See the graph here :  https://www.desmos.com/calculator/0mevks4btb

 

Note that as x increases, y decreases

 

 

 

cool cool cool

 
CPhill  Oct 13, 2017

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