Question 950808
Like you graph any other equation.
Choose x values, generate y values and plot the x-y pairs. 
Join the pairs with a curve.
{{{x=0}}},{{{y=-1*2^(0)=-1(1)=-1}}}
{{{x=1}}},{{{y=-1*2^(1)=-1(2)=-2}}}
{{{x=2}}},{{{y=-1*2^(2)=-1(4)=-4}}}
{{{x=3}}},{{{y=-1*2^(3)=-1(8)=-8}}}
{{{x=-1}}},{{{y=-1*2^(-1)=-1(1/2)=-1/2}}}
{{{x=-2}}},{{{y=-1*2^(-2)=-1(1/4)=-1/4}}}
{{{x=-3}}},{{{y=-1*2^(-3)=-1(1/8)=-1/8}}}
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{{{drawing(300,300,-6,6,-10,2,grid(1),
circle(0,-1,0.25),
circle(1,-2,0.25),
circle(2,-4,0.25),
circle(3,-8,0.25),
circle(-1,-1/2,0.25),
circle(-2,-1/4,0.25),
circle(-3,-1/8,0.25))}}}
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{{{drawing(300,300,-6,6,-10,2,grid(1),
circle(0,-1,0.25),
circle(1,-2,0.25),
circle(2,-4,0.25),
circle(3,-8,0.25),
circle(-1,-1/2,0.25),
circle(-2,-1/4,0.25),
circle(-3,-1/8,0.25),
graph(300,300,-6,6,-10,2,-1*2^x))}}}