Question 909276
{{{df/dx=(d/dx)(x^-2)}}}
{{{df/dx=-2x^-3}}}
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{{{df/dx}}} at 3 is {{{-2*(3)^-3=-2/27}}}.
Line containing that slope and (3,f(3)) is {{{y-f(3)=-(2/27)(x-3)}}}
{{{y-(1/9)=-(2/27)(x-3)}}}
{{{y-1/9=-(2/27)x+2/9}}}
{{{y=-(2/27)x+1/3}}}------One point is obviously (0, 1/3) and another would be (0,0).


Use the linear equation to find the x-axis intercept  (when y=0).


{{{0=-(2/27)x+1/3}}}
{{{(2/27)x=1/3}}}
{{{x=(27/2)(1/3)}}}
{{{x=9/2}}}-------The point being, ( 9/2, 0 ).


SUMMARY:
The triangle's points are ( 0,0 ),  ( 9/2, 0 ), and ( 0, 1/3 ).
Finish the area calculation.