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Functions - HSN forum

# Functions

7 replies to this topic

### #1davidmarsh01

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Posted 10 September 2009 - 03:21 PM

Hello, this is my first post so go easy on me . Could anyone help me with this functions question? The function f(x)=a/x +b is such that f(-1)=3/2 and f(2)=9. Find the values of a and b. Thanks for any help

### #2Marcus

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Posted 10 September 2009 - 03:29 PM

good al fashioned simultaneous equations
first substitute in the two points given to get two equations

-1=a/(3/2) + b
-1=2a/3 + b

and

2=a/9+b

and solve using simultaneous equations

answers should be , I think XD
a=-5.4, b =2.6

any other questions just post again

=-=-=Marcus=-=-=

### #3davidmarsh01

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Posted 10 September 2009 - 03:33 PM

QUOTE (Marcus @ Sep 10 2009, 04:29 PM) <{POST_SNAPBACK}>
good al fashioned simultaneous equations
first substitute in the two points given to get two equations

-1=a/(3/2) + b
-1=2a/3 + b

and

2=a/9+b

and solve using simultaneous equations

answers should be , I think XD
a=-5.4, b =2.6

any other questions just post again

I thought that if f(-1) = 3/2 then -1 would have to go in for the x term and 3/2 would go in for the f(x)? You seemed to do it the other way round?

### #4Marcus

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Posted 10 September 2009 - 04:02 PM

lol yeah you're right XD....I was em....testing you that's it
sorry XD
=-=-=Marcus=-=-=

### #5davidmarsh01

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Posted 10 September 2009 - 04:05 PM

QUOTE (Marcus @ Sep 10 2009, 04:29 PM) <{POST_SNAPBACK}>
good al fashioned simultaneous equations
first substitute in the two points given to get two equations

-1=a/(3/2) + b
-1=2a/3 + b

and

2=a/9+b

and solve using simultaneous equations

answers should be , I think XD
a=-5.4, b =2.6

any other questions just post again

and f(x)=3/2 it is the whole function that is equal to 3/2 not just the x as you subbed in

### #6davidmarsh01

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Posted 10 September 2009 - 04:09 PM

QUOTE (Marcus @ Sep 10 2009, 05:02 PM) <{POST_SNAPBACK}>
lol yeah you're right XD....I was em....testing you that's it
sorry XD

### #7davidmarsh01

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Posted 10 September 2009 - 04:18 PM

QUOTE (davidmarsh01 @ Sep 10 2009, 05:09 PM) <{POST_SNAPBACK}>
QUOTE (Marcus @ Sep 10 2009, 05:02 PM) <{POST_SNAPBACK}>
lol yeah you're right XD....I was em....testing you that's it
sorry XD

i have it! b=6.5 and a=5

### #8Sep

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Posted 10 September 2009 - 09:25 PM

i was having problems with this myself, this topic baffles me

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