P1 Maths Question Watch

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Leekey
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#1
Report Thread starter 16 years ago
#1
If anyone can solve the problem below can you please post me the solution.

Given That f(x) = (2x^3/2 - 3x^-3/2)^2 + 5

a) Find To 3.s.f the value of x for which f(x) = 5




I think that you put 5 in the place of f(x) which allows you to forget about the 5's as they are equal to eachother. Therefore you would put the difficult bit of the equation equal to 0. I have done this but always come up with an answer that is very incorrect.

P.S The Answer Should Be 1.14
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#2
Report 16 years ago
#2
(2x^3/2 - 3x^-3/2)^2+5=5
Take the 5 to the other side to get...
(2x^3/2 - 3x^-3/2)^2=0
Take the square root of 0 to get rid of the ^2 to get...
2x^3/2 - 3x^-3/2=0
Divide both sides by 2 to get...
x^3/2 - 1.5x^-3/2=0
Then take the - 1.5x^-3/2 to the other side giving
x^3/2=1.5x^-3/2
Divide the left hand side by x^-3/2 to give
x^3/2 / x^-3/2 = 1.5
Then subtract the powers (remember it's minus a minus so it becomes a plus) to give
x^3=1.5
Take the cube root of 1.5 and you should get 1.1446...

Hope that helps!
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Leekey
Badges: 9
#3
Report Thread starter 16 years ago
#3
Thanks for that !!!

I had been struggling with that for ages. The method I was tring involved me expanding the brackets rather that taking the root of it.

If One Of Those Comes Up In The Exam I'll Owe You Big

Cheers Agiain For THe Help
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#4
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#4
sorry to spoil it but as far as i've been taught to solve an equation for f(x) = 5 it means that when the equation = 0 a factor is (x-5) and you need to find the other factors. Its a factor theorem question,I think. X should have more than one answer as it is not a linear equation.

fee
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#5
Report 16 years ago
#5
you are wrong because i have the marks scheme and the answer he gave me was correct!!

I think you are thinking of a question where they will give you a function and a factor and ask you too fully factorise. This was not one of those because they are very simple 3 mark questions
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