Exercise · ZW-COMPLEX-TRIGONOMETRIC-FUNCTIONS-001 · ★☆☆ Basic
Compute \(\cos(i)\).
Choose one option.
Show answer
- A. \(\cosh 1=\dfrac{e+e^{-1}}{2}\)
Explanation
With \(z=i\): \(\cos i=\frac{e^{i\cdot i}+e^{-i\cdot i}}{2}=\frac{e^{-1}+e}{2}=\cosh 1\), a real number greater than 1.
Review the concept: Complex trigonometric functions
The sine \(\sin z\) and cosine \(\cos z\) of a complex number \(z\) are the functions that extend the real ones through the complex exponential \(e^{iz}\).
\[\sin z=\frac{e^{iz}-e^{-iz}}{2i},\qquad \cos z=\frac{e^{iz}+e^{-iz}}{2}\]
More practice problems: complex trigonometric functions
- ZW-COMPLEX-TRIGONOMETRIC-FUNCTIONS-002 For real y, what is sin (iy) equal to?
- ZW-COMPLEX-TRIGONOMETRIC-FUNCTIONS-003 What is sin ^2 z+cos ^2 z for any z∈ℂ?
- ZW-COMPLEX-TRIGONOMETRIC-FUNCTIONS-004 Which is a period of sin z on ℂ?
- ZW-COMPLEX-TRIGONOMETRIC-FUNCTIONS-005 Simplify sin (z+π).
- ZW-COMPLEX-TRIGONOMETRIC-FUNCTIONS-006 Compute sin \!((π)/(2)+iln 2).
- ZW-COMPLEX-TRIGONOMETRIC-FUNCTIONS-007 For positive real y, which value of y satisfies cos (iy)=2?
- ZW-COMPLEX-TRIGONOMETRIC-FUNCTIONS-008 Compute |sin (iln 2)|.
- ZW-COMPLEX-TRIGONOMETRIC-FUNCTIONS-009 What are all the zeros of sin z in ℂ?