(1)1=∫[-∞,+∞]f(x)dx=∫[0,1]xdx+∫[1,2](a-x)dx=x²/2 |[0,1]+(ax-x²/2)|[1,2]=1/2 -0+(2a-2)-(a-½)=a-1故a=2(2)E(X)=∫[-∞辩岩,+∞]xf(x)dx=∫宴扒[0,1]x²dx+∫[1,2](2x-x²)dx=x^3 /3|[0,1]+(x²携祥御-x^3/3)|[1,2]=1/3-0+(4-8/3)-(1-1/3)=1