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Complex Numbers and Applications- Advanced Engineering Mathematics

Decent Essays

Complex Numbers and Applications
ME50 ADVANCED ENGINEERING MATHEMATICS

1 Complex Numbers √ A complex number is an ordered pair (x, y) of real numbers x and y. For example, (−2.1, 3.5), (π, 2), (0, 0) are complex numbers. Let z = (x, y) be a complex number. The real part of z, denoted by Re z, is the real number x. The imaginary part of z, denoted by Im z, is the real number y. Re z = x Im z = y Two complex numbers z1 = (a1, b1) and z2 = (a2, b2) are equal, written z1 = z2 or (a1, b1) = (a2, b2) if and only if a1 = a2 and b1 = b2. For example, if (x, 2) = (3, c) then x = 3 and c = 2. Since a complex number is denoted by an ordered pair (x, y) of real numbers x and y, then we may view the complex number (x, y) as the point with abscissa x …show more content…

1. z = z 2. (cz) = cz 3. z1 + z2 = z 1 + z 2 4. z1z2 = z 1z 2 5. z1 z2

=

z1 z2

1.4 Forms of a complex number

The norm of a complex number z = (x, y), denoted by z is the real number z = x2 + y 2. For example, if z = (4, −3), then z = 42 + (−3)2 = 5. Observe that z is numerically equal to the distance from the point z in the complex plane to the origin (0, 0). A complex number with norm 1 is called a unit complex number. Some examples of unit complex √ √ 3 4 numbers are 5 , − 5 , (1, 0), 22 , 22 , (0, 1).
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Of particular importance to us are the unit complex numbers (1, 0) and (0, 1). Observe that (1, 0)(x, y) = (x, y) for all complex numbers (x, y). For this reason, we simply denote (1, 0) by 1. Let us denote the unit complex number (0, 1) by i. Then i2 = (0, 1)(0, 1) = (−1, 0) = (−1)(1, 0) = −(1, 0) = −1. Therefore, i2 = −1. The reason why 1 and i are important unit complex numbers is because every complex number can be written as a linear combination of them. To see this, let z = (x, y) be any complex number. Then z = (x, y) = (x, 0) + (0, y) = x(1, 0) + y(0, 1) =x·1+y·i = x + iy The form x + iy of the complex number (x, y) is called the Cartesian form. For example, the Cartesian form of (2, −3) is 2 − 3i. Operations on complex numbers become more convenient if we write complex numbers in Cartesian form and remember that i2 = −1. For example, to multiply (2, −3) and (−1, 2), we do it this way: (2, −3)(−1, 2) = (2 −

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