1.（2分之a+3分之b)(4分之1a^2-6分之1ab+9分之1b^2)
=(3a+2b)/6×(9a²-6ab+4b²)/36
=(3a+2b)(3a-2b)²/216
2.(4a^2-2分之5b^2)
=(8a²-5b²)/2