3m²-4m-21 = 0 的解法：解：Δ = 4²+4*3*21Δ = 268m1 = ( +4+√268 ) / (2*3)m1 = 3.3951175906242m2 = ( +4-√268 ) / (2*3)m2 = -2.0617842572908
