You need to include into the script:
// Create a function graph for f(x) = x**a1
var graph = brd.create('functiongraph',
[function(x){ return x**a1;}, -10.5, 10.5]
);
// Create a function graph for f(x) = x**a1
var graph = brd.create('functiongraph',
[function(x){ return x**a1;}, -10.5, 10.5]
);