向量b = (t, √3t)向量c = 向量a + t(向量b) = (t - 1/2, √3/2 + √3t)|向量c|² = (t - 1/2)² + (√3/2 + √3t)² = t² - t + 1/4 + 3t² + 3t + 3/4 = 4t² + 2t + 1= 4(t + 1/4)² + 3/4 t = -1/4, |向量c|取最小值√(3/4) = √3/2
