计算定积分,如图

(1)∫[1,2]1/x(x+1)dx=∫[1,2][1/x-1/(x+1)]dx=∫[1,2]1/xdx-∫[1,2]1/(x+1)dx=lnx|[1,2]-ln(x+1)|[1,2]=ln2-0-(ln3-ln2)=2ln2 -ln3(2)∫[-a,a]|x|dx=∫[-a,0]-xdx+∫[0,a]xdx=-1/2x^2|[-a,0]+1/2x^2|[0,a]=-1/2a^2+1/2a^2=0