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f(x)=2x+5                      g(x)x2-25

 

1. show that gf(x)=4x2 + 20x

 

 

2. solve gf(x)=g(7)

 

could you please explain how you got the answer, thanks.

Guest Mar 30, 2017
 #1
avatar+7324 
+3

f(x) = 2x + 5

and

g(x) = x2 - 25

 

So to find g( f(x) ), replace every x in g(x) with f(x) .

 

g( f(x) ) = (2x + 5)2 - 25

g( f(x) ) = (2x + 5)2 - 25

 

g( f(x) ) = (2x + 5)(2x + 5) - 25

g( f(x) ) = 4x2 + 10x + 10x + 25 - 25

g( f(x) ) = 4x2 + 20x

hectictar  Mar 30, 2017
edited by hectictar  Mar 30, 2017
 #2
avatar+7324 
+2

If g( f(x) ) = g( 7 ) , then that means f(x) must equal 7.

 

f(x) = 7

2x + 5 = 7

2x = 7 - 5

2x = 2

x = 1

hectictar  Mar 30, 2017

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