Let AD=x, BD^2=9-x^2
9(9-x)+49x=9[9-x^2+x(9-x)]
81-9x+49x=9[9-x^2+9x-x^2]
81+40x=9(-2x^2+9x+9)
81+40x=-18x^2+81x+81
18x^2-41x=0
x=41/18
BD^2=9-(41/18)^2
BD=sqrt[9-(41/18)^2]
你們都寫了最好的,我只寫個差一點的~~
kevin 寫到:AD=x
9-x2=49-(x2-18x+81)
x=sqrt(41/18)
BD=[sqrt9-(41/18)2]