Let p and q be two complex numbers such that q ≠ 0. If the roots of the equation x2+px+q2=0 have the same absolute value, then p/q is
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a
an integer
b
a rational number
c
a real number
d
a complex number.
answer is C.
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Detailed Solution
Let x1,x2 be the roots of x2+px+q2=0 and |x1|=|x2|=r. Note that x1x2=q2≠0. Now, p2q2=(x1+x2)2x1x2=x1x2+x2x1+2 =x1x2¯|x2|2+x1¯x2|x1|2+2=1r2(x1x2¯+x1¯x2)+2 =2r2Re(x1x¯2)+2⇒ p2q2 is a real number.Next, as −Re (x1 x¯2) ≤ |x1 x¯2| = |x1 x2|=|x1||x2|=r2,we get ⇒p2q2≥−2r2r2+2=−2+2=0Therefore, p/q is a real number.