The solution of
are 1 + 2i and 1 – 2i
<u>Solution:</u>
Given, equation is 
We have to find the roots of the given quadratic equation
Now, let us use the quadratic formula
--- (1)
<em><u>Let us determine the nature of roots:</u></em>
Here in
a = 1 ; b = -2 ; c = 5

Since
, the roots obtained will be complex conjugates.
Now plug in values in eqn 1, we get,

On solving we get,



we know that square root of -1 is "i" which is a complex number

Hence, the roots of the given quadratic equation are 1 + 2i and 1 – 2i
We must find UNIQUE combinations because choosing a,b,c,d... is the same as d,c,b,a...etc. For this type of problem you use the "n choose k" formula...
n!/(k!(n-k)!), n=total number of choices available, k=number of choices made..
In this case:
20!/(10!(20-10)!)
20!/(10!*10!)
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