028.34. a) $a^2 + (3a - b)^2$; б) $9p^2 - (q - 3p)^2$; в) $(5c + 7d)^2 - 70cd$; г) $(8m - n)^2 - 64m^2$.

a) $a^2 + (3a - b)^2 = a^2 + (9a^2 - 6ab + b^2) = 10a^2 - 6ab + b^2$ б) $9p^2 - (q - 3p)^2 = 9p^2 - (q^2 - 6pq + 9p^2) = 9p^2 - q^2 + 6pq - 9p^2 = -q^2 + 6pq$ в) $(5c + 7d)^2 - 70cd = (25c^2 + 70cd + 49d^2) - 70cd = 25c^2 + 49d^2$ г) $(8m - n)^2 - 64m^2 = (64m^2 - 16mn + n^2) - 64m^2 = -16mn + n^2$