Question 206750
<pre><font size = 4 color = "indigo"><b>
{{{2x^2+3xy-4y^2}}} when {{{x=2}}} and {{{y=-4}}}

Everywhere you see an {{{x}}} write {{{(2)}}} instead:
Everywhere you see a {{{y}}} write {{{(-4)}}} instead:


{{{2(2)^2+3(2)(-4)-4(-4)^2}}}

Do exponents first.  Replace {{{(2)^2}}} by {{{(4)}}}
Replace {{{(-4)^2}}} by {{{(16)}}}

{{{2(4)+3(2)(-4)-4(16)}}}

Do multiplications next:

Replace {{{2(4)}}} by {{{8}}}
Replace {{{3(2)(-4)}}} by {{{(-24)}}}
Replace {{{-4(16)}}} by {{{-64}}}

{{{8+(-24)-64}}}

{{{8-24-64}}}

{{{-80}}}

Edwin</pre>