Recall that for 
, we have
Replace 
with 
and we get
Lastly, multiply this by 
, so that
2nd degree with real coefients
so if a+bi is a root then a-bi is also a root
if 2+i is a root then 2-i is also a root
so, the factored form of a quadratic equation with roots r1 and r2 is
(x-r1)(x-r2)
so
2+i and 2-i
(x-(2+i))(x-(2-i))
(x-2-i)(x-2+i)
expanding we get
x²-4x+5
so c=5
Answer:
2 21/13
Step-by-step explanation:
