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# f(x) problem... watch

1. I am sitting my Standard Grades tomorrow, and have a small query, just to clarify something. Here is
a question from a past paper:

18. f(x) = 3? (not to the power n, but x, can't get it to work any other way!!)

(a) Find f(4) (Okay, done this)

(b) Given that f(x) = ?27, find x.

Can anyone help me to solve this?

Many Thanks!
2. [q1]> I am sitting my Standard Grades tomorrow, and have a small query, just to clarify something. Here[/q1]
[q1]> is a question from a past paper:[/q1]

[q1]> 18. f(x) = 3? (not to the power n, but x, can't get it to work any[/q1]
other
[q1]> way!!)[/q1]

What do you mean? Where does the question mark come from?

[q1]> (a) Find f(4) (Okay, done this)[/q1]
[q1]>[/q1]
[q1]> (b) Given that f(x) = ?27, find x.[/q1]
[q1]>[/q1]
[q1]> Can anyone help me to solve this?[/q1]
[q1]>[/q1]
[q1]> Many Thanks![/q1]

I think that you have neglected to give us the definition of the function
f(x).

Regards,

Richard Hayden.

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3. "Ally Morrison" <[email protected]> wrote:

[q1]>I am sitting my Standard Grades tomorrow, and have a small query, just to clarify something. Here[/q1]
[q1]>is a question from a past paper:[/q1]
[q1]>[/q1]
[q1]>18. f(x) = 3? (not to the power n, but x, can't get it to work any other way!!)[/q1]

That didn't come through very well. Ideally you should render your formulae in ascii.

I suspect you meant something like f(x) = 3 to the power of x, i.e.
f(x) = 3^x, is that right?

[q1]>[/q1]
[q1]>(a) Find f(4) (Okay, done this)[/q1]

f(4) = 3^4 = 81
[q1]>[/q1]
[q1]>(b) Given that f(x) = ?27, find x.[/q1]

That would be f(x) = 27, i.e. 3 to the power of x = 27. what is x?

The general method to solve this kind of question is to take logs:

log (3^x) = log (27)

but log (3^x) = x * log (3)

so x * log(3) = log(27), and x = log(27) / log(3) = 3

Gareth

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