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k can have any value; however, the range of values permitted depends upon different things:

The value of k depends on the value of x (ie given a value of x, the value of k can be calculated so that kx² + 4x + 5 = 0 has a root at that value of x):

kx² + 4x + 5 = 0

=> kx² = - 4x - 5 = -(4x + 5)

=> k = -(4x + 5)/x²

Note that if x = 0, then the value of k is not determinable.

Another possible answer using the discriminant of b²-4ac; from this the number of roots of the equation can be discovered:

Two real roots:

b²-4ac > 0

→ 4² - 4×k×5 > 0

→ 16 - 20k > 0

→ 20k < 16

→ k < 4/5

So for all values of k less than 4/5 there are two real roots of the quadratic kx² +4x + 5 = 0

One real repeated root:

b² - 4ac = 0

→ k = 4/5

So for k = 4/5, the quadratic (4/5)x² +4x +5 = 0 (→ 4x² +20x + 25 = 0) has one repeated real root.

Two complex roots:

b² - 4ac < 0

→ k > 4/5

So for all values of k greater than 4/5 there are two complex roots of the quadratic kx² +4x + 5 = 0

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9y ago

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