设向量b=(x,y)
x^2 + y^2 = 1
4x + 3y = 5
消去y得到
25x^2 - 40x + 16 =0
解得
x1 = x2 = 4/5
所以
y1 = y2 = 3/5
向量b=(4/5, 3/5)