令t=x^2,t∈[0,+∞)
则原式：t^2-16t+36=0,解之得,t=8+2√7或8-2√7
则x^2=8+2√7或8-2√7
解之得x=√(8+2√7)或-√(8+2√7)或√(8-2√7)或-√(8-2√7)
x四次方-16x²+36=0
令t=x^2,t∈[0,+∞)
则原式：t^2-16t+36=0,解之得,t=8+2√7或8-2√7
则x^2=8+2√7或8-2√7
解之得x=√(8+2√7)或-√(8+2√7)或√(8-2√7)或-√(8-2√7)