因式分解
2a(y-z)-3b(z-y)
= 2a(y-z)+3b(y-z)
= (2a+ 3b)(y-z)
计算
5*3^4 + 4*3^4 + 9*3^2
= 5*3^4 + 4*3^4 + 3^4
= 3^4 * (5 + 4 + 1)
= 81 * 10
= 810