[(a+2b)(a-2b)-(a-4b)^2]\4b其中a=5,b=2

[(a+2b)(a-2b)-(a-4b)^2]\4b其中a=5,b=2
[(a+2b)(a-2b)-(a-4b)^2]\4b其中a=5,b=2

[(a+2b)(a-2b)-(a-4b)^2]\4b其中a=5,b=2
解
[(a+2b)(a-2b)-(a-4b)²]÷4b
=[(a²-4b²)-a²+8ab-16b²]÷4b
=(8ab-20b²)/4b
=2a-5b
=2×5-5×2
=0