3a的2次方乘a的4次方+2a乘a2的2次方乘a的4次方减去4a的5次方乘a的2次方=3a^6+2a^5×a^4-4a^7=3a^6+2a^9-4a^7
化简：3a的2次方乘a的4次方+2a乘a2的2次方乘a的4次方减去4a的5次方乘a的2次方=3a^6+2a^5*a^4-4aa^7=3a^6+2a^9-4a^7
