如图1,小明遇到这样一个问题:如图,在中,是中线,求的取值范围.他的做法是:延长到,使,连接,证明,经过推理和计算使问题得到解决.请回答:
(1)小明证明的判定理由是______;(填写“”或“”)
(2)的取值范围是______;
方法运用:
(3)如图2,是的中线,在上取一点,连接,使得,延长交于点.求证:;
(4)如图3,在中,为的中点,.求证:.
同类型试题
y = sin x, x∈R, y∈[–1,1],周期为2π,函数图像以 x = (π/2) + kπ 为对称轴
y = arcsin x, x∈[–1,1], y∈[–π/2,π/2]
sin x = 0 ←→ arcsin x = 0
sin x = 1/2 ←→ arcsin x = π/6
sin x = √2/2 ←→ arcsin x = π/4
sin x = 1 ←→ arcsin x = π/2
y = sin x, x∈R, y∈[–1,1],周期为2π,函数图像以 x = (π/2) + kπ 为对称轴
y = arcsin x, x∈[–1,1], y∈[–π/2,π/2]
sin x = 0 ←→ arcsin x = 0
sin x = 1/2 ←→ arcsin x = π/6
sin x = √2/2 ←→ arcsin x = π/4
sin x = 1 ←→ arcsin x = π/2