解;(1)(3a-2b)*(a+2b)=3a^2+4ab-4b^2=3*3^2+4*3*4*cos3/4π-4*4^2=27-24√2-64＝-37-24 √ 2（2）a+b=√(a+b)^2 = √a^2+b^2+2ab=√9+16+2*3*4*cos3/4π=√25+12√ 2
