2a−3b2a - 3b2a−3b^2 = 2a−3b2a - 3b2a−3b2a−3b2a - 3b2a−3b = 2a2a2a2a - 2a3b3b3b - 3b2a2a2a + 3b3b3b3b = 4a^2 - 6ab - 6ab + 9b^2= 4a^2 - 12ab + 9b^2
2a−3b2a - 3b2a−3b^2 = 2a−3b2a - 3b2a−3b2a−3b2a - 3b2a−3b = 2a2a2a2a - 2a3b3b3b - 3b2a2a2a + 3b3b3b3b = 4a^2 - 6ab - 6ab + 9b^2
= 4a^2 - 12ab + 9b^2