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I don't even know what to call this.

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Here's my problem for today:

If f(x) = {(2,3),(4,5),(7,2)} and g(x) = {(2,1),(3,2),(7,4)}, then determine (f+g)(2) and (f(g(7)).

I have no clue how to do this. Help please!

ThisGuy  Jun 26, 2015

#1
+85958
+10

(f + g)(2)  =  f(2)  + g(2)   .........notce that   f(2) means that we are just asking what "y" value is associated with x in the function "f" when x = 2  ......this is the point (2,3)......so  f(2)  = 3

Likewise, g(2)   = 1

So......  (f + g)(2) = f(2) + g(2)  =  3 +  1 =   4

--------------------------------------------------------------------------------------------------------------------------

f(g(7)).....this means that, first, we are putting "7" into "g"  an finding the y value associated with that x value.....this is the point (7,4)....so   g(7) = 4

So....so far  ......f(g(7))  =  f(4).....now.......we are putting "4" into "f" and finding the y value associated with that x value.......this is the point (4,5)......so f(4)  = 5

To recap......f(g(7)  = f(4)  = 5

These are known as "composite" functions.....I'll admit they ARE a little tough to grasp !!!!

Post some more questions if you get stuck.....!!!

CPhill  Jun 26, 2015
Sort:

#1
+85958
+10

(f + g)(2)  =  f(2)  + g(2)   .........notce that   f(2) means that we are just asking what "y" value is associated with x in the function "f" when x = 2  ......this is the point (2,3)......so  f(2)  = 3

Likewise, g(2)   = 1

So......  (f + g)(2) = f(2) + g(2)  =  3 +  1 =   4

--------------------------------------------------------------------------------------------------------------------------

f(g(7)).....this means that, first, we are putting "7" into "g"  an finding the y value associated with that x value.....this is the point (7,4)....so   g(7) = 4

So....so far  ......f(g(7))  =  f(4).....now.......we are putting "4" into "f" and finding the y value associated with that x value.......this is the point (4,5)......so f(4)  = 5

To recap......f(g(7)  = f(4)  = 5

These are known as "composite" functions.....I'll admit they ARE a little tough to grasp !!!!

Post some more questions if you get stuck.....!!!

CPhill  Jun 26, 2015

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