#30 Measure Your Calibre

Algebra Level 4

{ sin ( log 2 z ) > 0 z < 1 \large{\begin{cases} \sin (\log_2|z|) > 0 \\ |z|<1 \end{cases}}

If A A be the total area satisfied by the region of the curves as shown above. Find the sum of all the integral solutions of x 2 4 + x 2 1 = A + 3 |x^2-4|+|x^2-1|=\lfloor A+3 \rfloor , where z z is a complex number.

Where sine is in the 1st set of quadrants, Namely ( 0 π 2 0 \rightarrow \dfrac{\pi}{2} ), ( π 2 π \dfrac{\pi}{2} \rightarrow {\pi} ), ( π 3 π 2 \pi \rightarrow \dfrac{3\pi}{2} ), ( 3 π 2 2 π \dfrac{3\pi}{2} \rightarrow {2\pi} )


The answer is 0.

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2 solutions

Raunak Agrawal
Apr 10, 2017

You dont even need to calculate the value of A, since for every solution 'x' , there is a solution '-x' too since the equation is even in x or symmetric about x=0 , hence the sum of solutions would be zero independent of the value of A

Md Zuhair
Apr 10, 2017

We need to find the area satisfying both the curves

Now see sin ( log 2 z ) > 0 \sin(\log_2|z|)>0 means log 2 z \log_2|z| lies in ( 0 , π ) (0, \pi) .

\implies 0 < log 2 z < π 0 < \log_2|z| < \pi

\implies 1 < z < 2 π 1 < |z| < 2^{\pi}

Now see that another equation is z < 1 |z|<1 , but from the above curve we have got z > 1 |z|>1 . So , the area cannot be founded. It is simply 0 0 .

See these curves in desmos

So A = 0 A=0

\implies x 2 4 + x 2 1 = 0 + 3 |x^2-4|+|x^2-1|=\lfloor 0 + 3 \rfloor

\implies . x 2 4 + x 2 1 = 3 |x^2-4|+|x^2-1|= 3

Now lets try to divide them in intervals and solve these.

Case 1 When x 2 x \geq 2
\implies x 2 4 + x 2 1 = 3 o r x = 2 x^2-4+x^2-1 = 3 \space or \space x=2

Case 2 In the region 2 > x 1 2> x \geq 1 . \implies x 2 + 4 + x 2 1 = 3 -x^2+4+x^2-1=3 \implies x = 1 x=1 as here for any x x , we can satisfy, But we need the integral one,

Case 3 In the region 1 > x 1 1 > x \geq -1 .

\implies x 2 + 4 x 2 + 1 = 3 -x^2+4-x^2+1=3 \implies x = 1 x=-1 after solving

Case 4 Now again in the interval 1 > x 2 -1 > x \geq -2
\implies x 2 + 4 + x 2 1 = 3 -x^2+4+x^2-1=3 \implies There is no solutions

Case 5

When x 2 x \leq -2

x 2 4 + x 2 1 = 5 x^2-4+x^2-1=5

\implies x = 2 x=-2

So Adding all we get S u m = 0 Sum=0

You are wrong sir, the log term can also lie in (-2pi, -pi) , also in (-4pi, -3pi) , so u get infinite solutions, and calculating the area you get around 0.04 square units. However you dont even need to calculate the value of A , becuz for every solution of x, you have the additive inverse '-x' as a solution too since the function is even, hence the sum is zero, independent of value of A.

Raunak Agrawal - 4 years, 2 months ago

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No, i have mentioned above that it will work for only the first set of quadrants .. Now ? Am i correct?

Md Zuhair - 4 years, 2 months ago

@Md Zuhair You may ask the sum of modulus values of roots or product of the roots.

Kushal Bose - 4 years, 2 months ago

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