X4+1/X4=(X²+1/X²)²-2 X²+1/X²=(X+1/X)²-2=7 则(X²+1/X²)²-2=49-2=47
(x+1/x)平方等于9,然后在平方就可以了
x+1/x=3∴x²+1/x²=(x+1/x)²-2=9-2=7x^4+1/x^4=(x²+1/x²)²-2=7²-2=47
47两边平方,再平方