Given the algebraic equation y = ax 3 + 7, which of the following, if any, are correct C++ statements for this equation?

a) y = a * x * x * x + 7;
b) y = a * x * x * ( x + 7 );
c) y = ( a * x ) * x * ( x + 7 );
d) y = (a * x) * x * x + 7;
e) y = a * ( x * x * x ) + 7;
f) y = a * x * ( x * x + 7 );

Parts (a), (d) and (e).