數學問題1條(須列式)(10分)

A is (5,4)
因為B是位於x軸上, 所以B is (x,0)
let (5,0) be C ( 因為 (5,0)係岩岩係A 點既垂直下面 )
因為ab is 5,
所以,
AB^2 = AC^2 + BC^2 (pyth.theoerm) (唔知你識唔識呢條公式, 三角形最長個邊既2次方, 係另外個2條邊既2次方相加)
5^2 = 4^2 + BC^2
25 = 16 + BC^2
25-16 = BC^2
9 = BC^2
BC = 3

C is (5,0)
因為B is 5+3 or 5-3
所以B is (8,0) or (2,0)