Ответ:

1)(4d-1/2)(1/2+4d)=(4d-1/2)(4d+1/2)=16d²-1/4

2)(5/6a-b)(b+5/6a)=(5/6a-b)(5/6a+b)=25/36a²-b²

3)(1/2y-1/3x)(1/2y+1/3x)=(1/2y)²-(1/3x)²=1/4y²-(1/3x)²=1/4y²-1/9x²

4)(2/3m+3/4n)(2/3m-3/4n)=(2/3m)²-(3/4n)²=4/9m²-(3/4n)²=4/9m²-9/16n²