Question 1061210
{{{ a+b = 3 }}}   (given)
{{{ (a+b)^2 = a^2 + 2ab + b^2 = 3^2 = 9 }}}    (squared both sides)

{{{ ab = 6 }}}   (given)
{{{ 2ab = 12 }}}   (multiplied both sides by 2)

I hope you see it now?   Before proceeding, please study the equation above and the equation resulting from squaring both sides.   
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Can't we solve {{{ a^2 + 2ab + b^2 = 9 }}} for  {{{ a^2 + b^2 }}},  knowing {{{2ab=12}}} ?