Application questions, there are several trapezoidal area formula derivation process, what are they?

Application questions, there are several trapezoidal area formula derivation process, what are they?

S=S1+S2+S3
S1=l1*H/2;S3=l3*H/2;S2=H*L1
L2=l1+l2+l3;
So s = (L1 + L2) * H / 2