郭敦顒回答:
∵(1-x^20)/(1-x)=5
∴1-x^20=5-5x
x^20-5x+4=0,或x^20-5x=-4,
这属于一元高次方程求解的问题了,这种方程没有公式解法,
可用尝试—逐步逼近法求解,
当x=0.8时,x^20-5x=0.011529215-4=-3.988470785;
当x=0.802时,x^20-5x=0.012119547-4.01=-3.997880426;
当x=0.803时,x^20-5x=0.011529215-4.015=-4.002574585;
当x=0.8024时,x^20-5x=0.012241042-4.012=-3.999758958;
当x=0.8025时,x^20-5x=0.012271589-4.0125=-4.00022841;
当x=0.80245132时,x^20-5x=0.01225671-4.0122566
=-3.99999989;
…
已有网友用exce计算出x=0.802451324917584.