A simple example is:
x4-1=0
This factors into:
(x-1)(x+1)(x-i)(x+i)=0, so
x=1 OR x=-1 OR x=i OR x=-i
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Certain functions, when solving to find the zeros (value which makes the function equal zero), the only value which will work has an imaginary component. Note that a parabola (graph of a quadratic or 2nd order polynomial) can touch the x-axis at a single point, or 2 points or no points. If it does not touch or cross the x-axis, then the root (or zeros) of the function are complex with imaginary components.Technically, all real numbers are a subset of complex numbers, so all numbers are complex - but this is not how we normally refer to them. We usually say that a number is real, or it is imaginary, or it is complex.
2 does belong to the set of imaginary numbers. Any real number is also imaginary. Imaginary numbers are the set of all numbers that can be expressed as a +b*i where "i" is the square root of negative one and "a" and "b" are both real numbers.
Any integer is a real, ...-3,-2,-1,0,1,2,3,4... etc, as they have no imaginary component.
If the equation of the parabola isy = ax^2 + bx + c then the roots are [-b +/- sqrt(b^2-4ac)]/(2a)
You need to be more specific. A quadratic equation will have 2 solutions. The 2 solutions can be equal (such as x² + 2x + 1 = 0, solution is -1 and -1). If one of the solutions is a real number, then the other solution will also be a real number. If one of the solutions is a complex number, then the other solution will also be a complex number. [a complex number has a real component and an imaginary component]In the equation: Ax² + Bx + C = 0. The term [B² - 4AC] will determine if the solution is a double-root, or if the answer is real or complex.if B² = 4AC, then a double-root (real).if B² > 4AC, then 2 real rootsif B² < 4AC, then the quadratic formula will produce a square root of a negative number, and the solution will be 2 complex numbers.If B = 0, then the numbers will be either pure imaginary or real, and negatives of each other [ example 2i and -2i are solutions to x² + 4 = 0]Example of 2 real and opposite sign: x² - 4 = 0; 2 and -2 are solutions.