Maths - 2 questions Watch

Searcher1
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#1
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1. For all values of x,
f(x)=x+5, g(x)=x^2-2
Solve fg(x)=gf(x)

2. y is directly proportional to x^2
When x=3, then y=36
a) express y in terms of x (answer not needed for a)

z is inversely proportional to x
When x=4, z=2
b)Show that z=c y^n, where c and n are numbers and c>0. You must find the values of c and n.
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RDKGames
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(Original post by Searcher1)
1. For all values of x,
f(x)=x+5, g(x)=x^2-2
Solve fg(x)=gf(x)

2. y is directly proportional to x^2
When x=3, then y=36
a) express y in terms of x (answer not needed for a)

z is inversely proportional to x
When x=4, z=2
b)Show that z=c y^n, where c and n are numbers and c>0. You must find the values of c and n.
Go on then.

If you want your answers checked then just post them here.
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Searcher1
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(Original post by RDKGames)
Go on then.

If you want your answers checked then just post them here.
x^2-2+5=x^2+10x+25-2
0=10x+20
-20=10x x=-2 ok But I do not have a clue about 2 b)
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Searcher1
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This task is from Method Maths, incidentally
(Original post by Searcher1)
x^2-2+5=x^2+10x+25-2
0=10x+20
-20=10x x=-2 ok But I do not have a clue about 2 b)
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Muttley79
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(Original post by Searcher1)
This task is from Method Maths, incidentally
What did you get for (a)?
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Searcher1
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I got:
36=9 * k, k=4, so y=4x
(Original post by Muttley79)
What did you get for (a)?
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Muttley79
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(Original post by Searcher1)
I got:
36=9 * k, k=4, so y=4x
I think you mean y = 4x^2?

OK so start (b) by saying z = c/x and find c
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Searcher1
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c = 8
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Muttley79
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(Original post by Searcher1)
c = 8
Agreed - now link the two together but substituting x from the first into the second.
Last edited by Muttley79; 5 days ago
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Searcher1
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