Answers:
a = 1
b = 14
c = 65
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Explanation:
Let's focus on the root x = -7+4i
Add 7 to both sides, then square both sides. Then get everything to one side so 0 is on the other side.
x = -7+4i
x+7 = 4i
(x+7)^2 = (4i)^2
(x+7)^2 = 16i^2
(x+7)^2 = 16(-1)
(x+7)^2 = -16
(x+7)^2+16 = 0
If you were to follow those steps for the other root -7-4i, then you should get the same result. Solving (x+7)^2+16 = 0 leads to the two complex roots -7+4i and -7-4i.
Expand out that expression to get it into standard form
(x+7)^2+16
(x+7)(x+7)+16
x^2+7x+7x+49+16
x^2+14x+65
The equation is now in y = ax^2+bx+c form
a = 1
b = 14
c = 65
If you were to plug those a,b,c values into the quadratic formula, you'll find that it leads to the two given roots -7+4i and -7-4i.
