Question 172100
1.  In the first place, ALL quadratic equations have two roots -- The Fundamental Theorem of Algebra says so.  The question is, are the roots real numbers or not.  Use the discriminant to make the determination.


The discriminant is the part of the quadratic formula that is under the radical sign.


Quadratic formula:  {{{x = (-b +- sqrt( b^2-4*a*c ))/(2*a) }}} 


So the discriminant is:  {{{DELTA = b^2-4ac}}}


Use the discriminant to determine the character of the roots of a quadratic equation.


if {{{DELTA=0}}} there is one real number root with a multiplicity of 2.


if {{{DELTA>0}}} there are two real number roots.


if {{{DELTA<0}}} there is a conjugate pair of complex roots of the form {{{a+-bi}}} 


I'll do the first one, and then you can do the rest:


{{{x^2 + 6x - 7 = 0}}}


Here, {{{a=1}}}, {{{b=6}}}, and {{{c=-7}}}, so {{{DELTA=6^2-4(1)(-7)=36+28=64>0}}} so there are two real number roots.


Simple as that.  You can do the rest.


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2.  To be exactly correct, this problem is incorrectly stated.  {{{x}}} cannot simultaneously be {{{1}}} AND {{{-8}}}.  {{{x=1}}} <b>OR</b> {{{x=-8}}}.


Here's the rule:  {{{a}}} is a root of a polynomial equation if and only if {{{x-a}}} is a factor of the polynomial.


Since {{{x=1}}} <b>OR</b> {{{x=-8}}} are roots of the desired quadratic, then {{{x-1}}} and {{{x+8}}} must be factors of the quadratic polynomial, so just multiply {{{(x-1)(x+8)}}} and set the result equal to zero.


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3.  This one is answered in the discussion for problem 1 above.


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4.  No idea how to answer this one.  You get zeros at -4 and 7, and a minimum value at 1.5  Your guess is as good as mine.