p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; line-height: 18.0px; font: 16.0px 'Songti SC'; color: #000000; background-color: #ffffff} p.p2 {margin: 0.0px 0.0px 0.0px 0.0px; line-height: 18.0px; font: 16.0px 'Songti SC'; color: #000000; background-color: #ffffff; min-height: 22.0px} span.s1 {font-kerning: none} AD = (b^2 - x^2)^(1/2), BD = (a^2 - x^2)^(1/2), AB = (b^2 - x^2)^(1/2)+(a^2 - x^2)^(1/2) AC^2 + BC^2 = AB^2 b^2 + a^2 = ((b^2 - x^2)^(1/2)+(a^2 - x^2)^(1/2))^2 i.e. b^2+a^2= (b^2 - x^2)+2((b^2 - x^2)(a^2- x^2))^(1/2) + (a^2 - x^2) i.e. x^2 =((b^2 - x^2)(a^2- x^2))^(1/2) i.e. 0 = a^2*b^2 -a^2*x^2 - b^2*x^2 i.e. 0 = 1/x^2 - 1/b^2 - 1/a^2 QED 谷歌先生,题目怎么越出越容易啦? |