а) (x-2y)(x+2y)+4y^2 = x^2 - 4y^2 + 4y^2 = x^2
б) (3x-4y)^2 - (2x-7y)(4x+2y) = (3x-4y)(3x-4y) - (2x-7y)(4x+2y= 9x^2 - 12xy - 12xy + 16y^2 - (8x^2 - 28xy + 16xy - 14y^2= 9x^2 - 24xy + 16y^2 - 8x^2 + 42xy - 14y^= x^2 + 18xy + 2y^2
а) (x-2y)(x+2y)+4y^2 = x^2 - 4y^2 + 4y^2 = x^2
б) (3x-4y)^2 - (2x-7y)(4x+2y) = (3x-4y)(3x-4y) - (2x-7y)(4x+2y
= 9x^2 - 12xy - 12xy + 16y^2 - (8x^2 - 28xy + 16xy - 14y^2
= 9x^2 - 24xy + 16y^2 - 8x^2 + 42xy - 14y^
= x^2 + 18xy + 2y^2