原式 = (1/9) ∫ [0,16](√(x+9) + √x ) dx
= (1/9) * (2/3) {[(x+9)^(3/2) + x^(3/2)] | (x=16) -[(x+9)^(3/2) + x^(3/2)] | (x=0) }
= (2/27) ( 125 + 64- 27) = 12