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an equation with imaginary roots is: a)    x^2-2x-5=0 b)    x^2+2x+5=0...

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swavers | Student, Grade 11 | eNoter

Posted March 16, 2011 at 1:24 AM via web

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an equation with imaginary roots is:

a)    x^2-2x-5=0

b)    x^2+2x+5=0

c)    x^2-2x+5=0

d)   x^2+2x-5=0

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justaguide | College Teacher | (Level 2) Distinguished Educator

Posted March 16, 2011 at 2:08 AM (Answer #1)

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If a quadratic eqaution ax^2 + bx + c = 0 has imaginary roots, b^2 - 4ac < 0.

For

a) x^2 - 2x - 5 = 0 : 4 + 20 = 24 > 0

b) x^2 + 2x + 5 = 0: 4 - 20 = -16 < 0

c) x^2 - 2x + 5 = 0 : 4 - 20 = -16 < 0

d) x^2 + 2x - 5 = 0 : 4 + 20 = 24 > 0

Therefore the options b and c have imaginary roots.

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