∴θ 1=∠A2A 1A3=2θ，

∴θ2=∠A2A4A3=θ+2θ=3θ，

∴θ3=∠A2A4A3+θ=4θ，

So the answer is θ 1=2θ, θ2=3θ, θ3=4θ,

(4) According to the meaning of the question, 5 θ ≤ 90.

{

6θ>90 ,

∴ 15 ≤θ< 18 .