(5a+3b)^2=(5a-3b)^2+4*5a*3b所以A=4*5a*3b=10*3a*2bA-(3a-2b)^2=10*3a*2b-9a^2+2*3a*2b-4b^2 =12*3a*2b-9a^2-4b^2 =72ab-9a^2-4b^2