已知a=1/2,b=2/3,求代数式5a[(a^2+4ab+4b^2)/(a+2b)+(9a^2-16a^2)/(3a-4b)]的值

5a[(a^2+4ab+4b^2)/(a+2b)+(9a^2-16b^2)/(3a-4b)]
=5a[(a+2b)^2/(a+2b)+(3a+4b)(3a-4b)/(3a-4b)]
=5a(a+2b+3a+4b)
=10a(2a+3b)
=10*1/2(2*1/2+3*2/3)
=5(1+2)
=15