a的平方减a减1得0,求a的8次方加7乘a的负4次方
问题描述：
a的平方减a减1得0,求a的8次方加7乘a的负4次方
答
a²-a-1=0,a²=a+1,a^4=a²+2a+1=a+1+2a+1=3a+2a^8=(3a+2)²=9a²+12a+4=21a+13a^8+7*a^(-4)=21a+13+7*1/a^4=21a+13+7/(3a+2) =(63a²+81a+33)/(3a+2) =(144a+96)/(3a+2) =48(3a+2)/(3a+2) ...