№4
1) 3(1+2xy)(1-2xy)=3(1-4x²y²)=3-12x²y²
2) (x²-y²)²=x^4-2x²y²+y^4
3) (a+b)²-(a-b)²=a²+2ab+b²-a²+2ab-b²=a²+2ab+b²-a²+2ab-b²=2ab+2ab=4ab
№5
a) (4x-3)(4x+3)-(4x-1)^2=3x
16x²-9-(16x²-8x+1)=3x
16x²-9-16x²+8x-1=3x
-10+8x=3x
8x-3x=10
5x=10
x=2
б) 16с²-49=0
(4c-7)(4c+7)=0
4c-7=0 4c+7
4c=7 4c= - 7
c=7/4 c= - 7/4
c=1,75 c= - 1,75