determine a,b and c such that formula _

/ h

| f(x) dx = h(af(0) + bf(h / 3) + cf(h))

_/ 0

is exact for polynomial of as high order as possible.Also determine the order of truncation error

for the first part i am confused on which order to take whether n=2 or n=3.

After that i tried determing a,b,c by legendres polynomial as i have got x(0)=0 x(1)=h/3 x(2)=h

is my method correct? please help