Question

find the mass of the bar [AB] using the density f(x,y)=x and A(1,0), B(3,1)

Answer 1

Well the mass is given by:
\[\int\limits \rho dV\]
And since the density is only a function of x you only need to integrate from 1 to 3.
\[\int\limits_1^3 \rho(x)dx\]