Check the 1st picture below.
well, from the picture, we can see that when x = 0, y = 100, also that when x = 1, y = 50.
let's recall that an exponential equation is in the form of y = abˣ.
[tex]\bf y = ab^x \\\\[-0.35em] ~\dotfill\\\\ (\stackrel{x}{0}~~,~~\stackrel{y}{100})\qquad 100 = ab^0\implies 100=a(1)\implies \boxed{100=a} \\\\[-0.35em] ~\dotfill\\\\ (\stackrel{x}{1}~~,~~\stackrel{y}{50})\qquad y=ab^x\implies y = 100b^x\implies 50 =100b^1 \\\\\\ 50=100b\implies \cfrac{50}{100}=b\implies \boxed{\cfrac{1}{2}=b} \\\\[-0.35em] \rule{34em}{0.25pt}\\\\ ~\hfill y = 100\left( \frac{1}{2} \right)^x~\hfill[/tex]
now, if you graph that in your graphing calculator, it'd be more or less like the 2nd picture below.
