1)
a) (7a+4)² = 49a²+56a+16
б) (3x-b)² = 9x²-6bx+b²
в) (b+5)(b-5) = b²-25
г) (3y-2x)(3y+2x) = 9y² - 4x²
2) (c+b)(c-b)-(7c²-b²) = c²-b²-7c²+b² = c²-7c² = -6c²
3)
a) 81y²-a² = (9y-a)(9y+a)
б)c²+24bc+144b² = c²+2*c*12b+12²b² = c²+2*c*12b+(12b)² = (c+12b)²