Solve for z in the equation sin(z) = 2

Note that |sin(x)| <= 1 for all real x, so our solution must be complex if one exists at all
Euler's formula gives that exp(ix) = cos(x) + isin(x), and hence exp(-ix) = cos(x) - isin(x) since cos is even (so cos(-x) = cos(x)), and sin is odd (and so sin(-x) = -sin(x)).
Thus combining the two equations yields the identity sin(z) = (1/(2i))(exp(iz) - exp(-iz))
Remember that we are solving for sin(z) = 2, so proceed by writing w for exp(iz) and we have that
w - (1/w) = 4i noting that exp(-iz) = 1/(exp(iz)) = 1/w
Multiplying by w yields the quadratic in w: w^2 - 4wi - 1 = 0 and solving gives w = i(2 ± sqrt(3))
Writing z = x + iy where x, y are real, we see that w = exp(iz) = exp(i(x + iy)) = exp(-y + ix) = exp(-y)(cos(x) + isin(x))
Hence equating real and imaginary parts with the known values of w, we see that exp(-y)cos(x) = 0, and since exp is non-negative for any real argument, it must be that cos(x) = 0 and so x = (pi/2) + n(pi) where n is any integer
Now we deal with y, which is slightly more tricky. we have that exp(-y)sin(x) = 2 ± sqrt(3)
Note that when cos(x) = 0, sin(x) = 1 or -1, in fact sin(x) = 1 when x = (pi/2) + 2n(pi), sin(x) = -1 when x = (pi/2) + (2n+1)(pi)When sin(x) is negative, exp(-y) is negative and hence has no solution since y is real.
Thus we find the x = (pi/2) + 2n(pi), and y = log(2 ± sqrt(3))
Hence the final solution is z = (pi/2) + 2n(pi) + i(log(2 ± sqrt(3))

SL
Answered by Sam L. Further Mathematics tutor

6699 Views

See similar Further Mathematics A Level tutors

Related Further Mathematics A Level answers

All answers ▸

Given that α= 1+3i is a root of the equation z^3 - pz^2 + 18z - q = 0 where p and q are real, find the other roots, then p and q.


A curve has polar equation r = 1 + cos THETA for 0 <= THETA <= 2Pi. Find the area of the region enclosed by the curve


Further Maths: How do you find the inverse of a 2 x 2 matrix?


Find the complex number z such that 5iz+3z* +16 = 8i. Give your answer in the form a + bi, where a and b are real numbers.


We're here to help

contact us iconContact usWhatsapp logoMessage us on Whatsapptelephone icon+44 (0) 203 773 6020
Facebook logoInstagram logoLinkedIn logo

© MyTutorWeb Ltd 2013–2025

Terms & Conditions|Privacy Policy
Cookie Preferences