已知x乘以x的n-1次方乘以x的2n次方=x的15次方
x的(1+n-1+2n)次方=x的15次方
1+n-1+2n=15
3n=15
n=52乘以n得2次方-n
=2X5的2次方-5
=2X25-5
=50-5
=45