已知三分之一xyz平方乘N=(5/3)x^(4n+1-2n-1)*y^(n+3-n+1)*z^5
=(5/3)x^(2n)*y^4z^5
所以N=3(5/3)*x^(2n-1)y^(4-1)*z^(5-2)
即N=5x^(2n-1)*y^3*z^3