49(a+b)^2-16(b-a)^2
=[7(a+b)+4(b-a)][7(a+b)-4(b-a)]
=(7a+7b+4b-4a)(7a+7b-4b+4a)
=(3a+11b)(3b+11a)
（a-b)(3a+b)^2+(a+3b)^2(b-a)
=(a-b)(3a+b)^2-(a+3b)^2(a-b)
=(a-b)[(3a+b)^2-(a+3b)^2]
=(a-b)(3a+b+a+3b)(3a+b-a-3b)
=(a-b)(4a+4b)(2a-2b)
=8(a-b)^2(a+b)
9(a-b)^2+12(a^2-b^2)+4(a+b)^2
=[3(a-b)]^2+2×3×2(a-b)(a+b)+[2(a+b)]^2
=[3a-3b+2a+2b]^2
=(5a-b)^2
25x(0.4-y)^2-10y(y-0.4)^2,其中x=0.04.y=2.4
=25x(0.4-y)^2-10y(0.4-y)^2
=(25x-10y)(0.4-y)^2
=5(5x-2y)(0.4-y)^2
=5(0.2-4.8)(0.4-2.4)^2
=5*(-4.6)*4
=20*(-4.6)
=-92
（a^2+b^2)^2-4a^2b^2,其中a=3.5,b=1.5
=a^4+b^4+2a^2b^2-4a^2b^2
=a^4+b^4-2a^2b^2
=(a^2-b^2)^2
=(a+b)^2(a-b)^2
=(3.5+1.5)^2(3.5-1.5)^2
=5^2*2^2
=25*4
=100