Question 1180749

Given the expression;{{{ x^2 - kx + 81}}}

a) Determine the value of "{{{k}}}" that makes it a perfect square trinomial


recall the rule: {{{(a - b)^2=a^2-2ab+b^2}}}


in your case {{{a=1}}}, {{{2ab=k}}}, {{{b^2=81}}}=>{{{b=9}}}

{{{k=2*1*9}}}
{{{k=18}}}


{{{x^2 - 18x + 81}}}
{{{x^2 - 18x + 9^2}}}
{{{(x - 9)^2}}}

b) Factor it to prove it is factorable.

{{{(x - 9)(x-9)}}}