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February 27, 2015

February 27, 2015

Posted by **toni** on Tuesday, October 8, 2013 at 12:52pm.

Consider the quadratic expression X^2 + 4x + c = 0.

For what range of values does the equation have two complex roots?

what am i doing here can someone show me step by step so i can at least try to do the other problems i have

- algebra -
**Jai**, Tuesday, October 8, 2013 at 1:01pmHi. I answered you previous post and it was almost similar, except that here, the roots must be complex/imaginary so D must be less than zero. Anyway,

Recall the formula for discriminant. For a quadratic equation in the general form, ax^2 + bx + c = 0,

D = b^2 - 4ac

if

D = 0 : real, equal/double root

D > 0 : two real, unequal roots

D < 0 : two imaginary roots

Since we're required to have complex/imaginary, D < 0, and solve for the unknown, c.

x^2 + 4x + c = 0

a = 1

b = 4

c = ?

Substituting to the discriminant formula, (D < 0)

0 < 4^2 - 4*1*c

0 < 16 - 4c

4c < 16

c < 4

Hope this helps~ :3

- algebra -
**Swaastikaa**, Friday, October 11, 2013 at 3:32amI disagree that the answer is c < 4. The correct answer is c > 4.

Lets see the steps again:

x^2 + 4x + c = 0, b^2 - 4ac < 0

4^2 - 4(1)(c) < 0

16 - 4c < 0

16 < 4c

4c > 16

Therefore c > 4

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