Відповідь:(a+3)(a-3)-2a(4+a)=a²-9-8a+2a²

(2a+1)(2a-1)+(a-7)(a+7)=4a²-1+a²-49

(4x-3y)(4x+3y)+(3x+4y)(4y-3x)=8x²-9y²+(4y+3x)(4y-3x)=8x²-9y²+8y²-9x²

(y-3)(5-y)-(4-y)(y+4)=5y-y²-15+3y-(4-y)(4+y)=5y-y²-15+3y-(8-y²)=5y-y²-15+3y-8+y²