10m^2+9m-12
=10[m^2+9/10m+(9/20)^2-81/400-1.2]
=10[(m+9/20)^2-561/400]
=10(m+9/20+√561/20)(m+9/20-√561/20).
写作业时,可把同分母两数写成一个式子.