Thursday, October 1, 2015

Determine m if the function f has two real roots. The roots are not equal. f = mx^2 + (m-1)*x - m + 2

The function f(x) has 2 distinct real roots if and only if
the discriminant delta is strictly positive.


delta = b^2 -
4ac


We'll identify a, b and
c.


a = m


b = m -
1


c = 2 - m


delta = (m-1)^2 -
4*m*(2 - m)


We'll impose the constraint: delta >
0


(m-1)^2 - 4*m*(2 - m) >
0


We'll expand the square and remove the
brackets:


m^2 - 2m + 1 - 8m + 4m^2 >
0


We'll combine like
terms:


5m^2 - 10m +
1>0


Now, we'll determine the roots of the expression
5m^2 - 10m + 1.


5m^2 - 10m + 1 =
0


We'll apply the quadratic
formula:


m1 =
[10+sqrt(100-20)]/10


m1 =
(10+4sqrt5)/10


m1 =
(5+2sqrt5)/5


m2 =
(5-2sqrt5)/5


The expression is positive
outside the roots, namely when m belongs to the
intervals:


(-infinite ,
(5-2sqrt5)/5) U ((5+2sqrt5)/5 , +infinite).

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