解[30-(x-10)]^2
=[30-x+10]^2
=（40-x）^2
=（x-40）^2
=x^2-80x+1600x²+20²=30-(x-10)]²？？？（偶公式弄混了，怎算）是解方程吗？解由x²+20²=[30-(x-10)]² 得x^2+400=x^2-80x+1600即80x=1200解得x=15