設$\sqrt{2}=1.5 - y，$則$(1.5 - y)^2 = 2。$
展開得：$1.5^2 - 2×1.5× y + y^2 = 2，$
即$2.25 - 3y + y^2 = 2。$<br>
忽略$y^2$（$y$較小，$y^2$更?。?，
得$2.25 - 3y \approx 2。$
解得：$3y \approx 2.25 - 2 = 0.25，$
$y \approx 0.25÷3 \approx 0.0833。$
則$\sqrt{2}=1.5 - y \approx 1.5 - 0.0833 = 1.4167，$精確到$0.001$為$1.417。$
