1) (a-b)^2= a^2 - 2*a*b + b^2
2) x^2 - 2xy +y^2 = (x-y)^2
3) m^2 - 3mn + n^2 - невозможно
4) (2n-3)^2 = (2n)^2 - 2*2n*3 + 3^2 = 4 n^2 - 12n + 9
5) a^2 - 4a +4 = (a-2)^2
6) (x-y)^2 = x^2 - 2xy + y^2
7) a^2 - 2ab + b^2 = (a-b)^2
8) p^2 - 4pq + q^2 - невозможно
9) (2-3k)^2 = 4 - 12k + 9 k^2
10) a^2 - 6a + 9 = (a-3)^2
11) (c-d)^2 = c^2 - 2cd + d^2
12) 1 - 2x + x^2 = (1-x)^2
13) a^2 - 8a + 16 = (a-4)^2
14) (2p-q)^2 = 4p^2 - 4pq + q^2
15) 4a^2 - 4a + 1 = (2a - 1)^2