Question 101757
{{{ax^2+bx+c=0}}} has one root if and only if {{{b^2-4ac=0}}}


Since {{{2x^2-kx+5=0}}} has one real root, then,

{{{(-k)^2-4*2*5=0}}}
{{{k^2-40=0}}}
{{{k^2=0+40}}}
{{{k^2=40}}}
{{{k= 0+-sqrt(40)}}}
{{{k=0+-sqrt(4*10)}}}
{{{k=0+-sqrt(4)sqrt(10)}}}
{{{k=0+-2sqrt(10)}}}


thus, {{{k=2sqrt(10)}}} or {{{k=-2sqrt(10)}}}


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