Sunday, April 26, 2015

I need to solve the equation ((x+i) raise to n)+((x-i) raise to n)=0. i must use trigonometry but i don't know how. thanks

We'll re-write the
equation:


`(x+i)^n + (x-i)^n =
0`


We'll divide by `(x-i)^n`  both
sides:


`((x+i)/(x-i))^n + 1 =
0`


We'll subtract 1 both
sides:


`((x+i)/(x-i))^n = -1` We'll write -1 as a
trigonometric form of a complex number:


`-1 = cos pi + isin
pi`


We'll re-write the
equation:


`((x+i)/(x-i))^n = cos pi + isin
pi`


We'll remove the n-th power from the left side, raising
both sides to the power `(1/n):`


`` `(x+i)/(x-i) = (cos pi
+ isin pi)^(1/n)`


We'll apply Moivre's rule to the right
side:


`(x+i)/(x-i) = (cos ((2k+1)pi/n) + isin
((2k+1)pi/n))` k is an integer number.


We'll multiply the
denominator from the left side, by it's
conjugate:


`(x+i)^2/((x+i)(x-i)) = (cos ((2k+1)pi/n) + isin
((2k+1)pi/n))`


The difference of squares from denominator
returns the product `x^2 + 1` .


We'll cross multiply and
we'll get:


`x^2 + 2ix - 1 = (x^2 + 1)(cos ((2k+1)pi/n) +
isin ((2k+1)pi/n))`


`x^2 + 2ix - 1 = (x^2 + cos
((2k+1)pi/n)) + i(x^2*sin ((2k+1)pi/n) + sin
((2k+1)pi/n))`


We'll compare both
sides:


`x^2 - 1 = x^2 + cos
((2k+1)pi/n)`


`` `cos ((2k+1)pi/n) =
-1`


`` `2x = x^2*sin ((2k+1)pi/n) + sin
((2k+1)pi/n)`


`sin[((2k+1)pi/n]= (2x)/(x^2 +
1)`


`x_k = cot
[((2k+1)pi)/(2n)]`


Therefore, the solutions
of the given equation are: `x_k = cot [((2k+1)pi)/(2n)].`

No comments:

Post a Comment

What is the meaning of the 4th stanza of Eliot's Preludes, especially the lines "I am moved by fancies...Infinitely suffering thing".

A century old this year, T.S. Eliot's Preludes raises the curtain on his great modernist masterpieces, The Love...