先化简再求值：（x-2-5/x+2)÷(x-3/2x+4)【其中x=根号2-3】

原式=[(x-2)(x+2)-5]/(x+2)×(2x+4)/(x-3)
=(x²-4-5)/(x+2)×2(x+2)/(x-3)
=2(x²-9)/(x-3)
=2(x+3)(x-3)/(x-3)
=2(x+3)
=2(√2-3+3)
=2√2[(a+c)^2-b^2][(a-c)^2-b^2]怎么化到(a+b+c)(a-b+c)(a+b-c)(a-b-c)平方差