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# Maths Equation Help

I'm stuck on a piece of work, I've done everything apart from the very last bit.

I need to prove something...

I have to show the equation...

( (x-1)^2 ) / ( (sqrt(3)) * (sqrt(x^4 + 4x^2 +1)) )

Is always between 0 andf 1 when x isn't 1.

In other words the denominator is always greater than the numerator.

It's quite clear and I can show it graphically, but I need a proof for it which I'm stuck with.

When I say proof, it's not going to be anything complex at all.

Any advice would be appreciated.

James

:-s ???

Original Poster

It's for my Mechanics, got to prove two lines always intersect at an acute angle apart from when x=1

The equation is equal to cos(x) which needs to equal between 0 and 1 for the above statement to be true...

But not sure that will make it any clearer haha!

Far too intelligent for people on here mate :-p

When 'x' is 1, the numerator ((x-1)^2) is 0, hence the result of the equation is 0.

However, as 'x' increases above 1, the denominator ( (sqrt(3)) * (sqrt(x^4 + 4x^2 +1)) ) tends towards approximately double of the numerator (from x = 16 onwards the denominator is just slightly more than double of the numerator).

Hence, the result of the equation falls in the range 0.5 to 0.6 (to 1 decimal place).

As you are obviously aware, the Cosine of an angle is the ratio of the length of the Adjacent side to the length of the Hypotenuse.

Can you "prove" a Cosine of between 0.5 & 0.6 is an acute angle (one less than 90 degrees)?

BFN,

fp.

Original Poster

fanpages1 person likes this

When 'x' is 1, the numerator ((x-1)^2) is 0, hence the result of the … When 'x' is 1, the numerator ((x-1)^2) is 0, hence the result of the equation is 0.However, as 'x' increases above 1, the denominator ( (sqrt(3)) * (sqrt(x^4 + 4x^2 +1)) ) tends towards approximately double of the numerator (from x = 16 onwards the denominator is just slightly more than double of the numerator).Hence, the result of the equation falls in the range 0.5 to 0.6 (to 1 decimal place).As you are obviously aware, the Cosine of an angle is the ratio of the length of the Adjacent side to the length of the Hypotenuse.Can you "prove" a Cosine of between 0.5 & 0.6 is an acute angle (one less than 90 degrees)?.

Thank you very much for the reply!

I don't need to prove the cosine bit at all, just the first bit. Is there a way to prove algebraically what I've highlighted in bold as opposed to stating it? That's the bit I'm stuck on, I've got to show it for every positive and negative value of x that the numerator can never be greater than the denominator.

Cheers
James

Hello
I started doing somethings with your equation but due to lack of time and no further clue I am unable to go further at this time. May be this will help you. try this if it helps.

( (x-1)^2 ) / ( (sqrt(3)) * (sqrt(x^4 + 4x^2 +1)) )

Let us say that this is = n

( (x-1)^2 ) / ( (sqrt(3)) * (sqrt(x^4 + 4x^2 +1)) ) = n

Do a power of 2 on both sides

( ( (x-1)^2 ) / ( (sqrt(3)) * (sqrt(x^4 + 4x^2 +1)) ) )^ 2 = n ^ 2

( (x-1)^2 ) ^ 2 / ( (sqrt(3)) * (sqrt(x^4 + 4x^2 +1)) ^ 2 ) = n^2

( (x-1)^4 ) / ( (sqrt(3)) ^ 2 * (sqrt(x^4 + 4x^2 +1)) ^ 2 ) = n ^ 2

( (x-1)^4 ) / ( 3 * (x^4 + 4x^2 +1) ) = n ^ 2

( (x-1)^4 ) / ( 3x^4 + 12x^2 +3) ) = n ^ 2

OMG this has made me feel so thick, think I will stick with helping my 11 year old do fractions.

Goofeys Girl

OMG this has made me feel so thick, think I will stick with helping my 11 … OMG this has made me feel so thick, think I will stick with helping my 11 year old do fractions.

me too,i wish i never saw this grrrr

Original Poster

I tried doing it by putting it equal to something to no avail.

I've handed in what I did so will just wait and see now. Thank a lot for the help though.

James

Banned

this is a wind up isn´t it?