[(a + b) &# 178; - (a-b) &# 178; + 6A & # 178; B & # 179;] / (- 2Ab), where a = - 2, B = 1 If the circumference of △ DEF is 15, then the length of BC side is____

[(a + b) &# 178; - (a-b) &# 178; + 6A & # 178; B & # 179;] / (- 2Ab), where a = - 2, B = 1 If the circumference of △ DEF is 15, then the length of BC side is____

(1) [(a + b) [(a + b) [(a-b) [(a-b) [(a-b) [(a-b) [(a-b) [(a-b) [(a-b) \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\so: BC

Calculation: (A & # 178; - B & # 178;) / (a + b) + (A & # 178; - 2Ab + B & # 178;) / (a-b)

The original formula = (a + b) (a-b) / (a + b) + (a-b) & #178; / (a-b)
=a-b+a-b
=2a-2b

The result of operation is 1-2ab & # 178; + A & # 178; B ^ 4 is ()
A.（-1+ab²）²
B.（1+ab²）²
C.（-1+a²b²）²
D.（-1-ab）²
Requirement: write out the process of ABCD

The result of the operation is 1-2ab and the result is 1-2ab and the result is 1-2ab and the result is 1-2ab and the result is 1-2ab and the result is 1-2ab and 178; + A and the result of B ^ 4 is the result of (a) (- 1 + AB & \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\;) & #178; = 1-2a & #178; B & #17