Substitute the points (cosα, sinα) into the linear equation, with cos α/a+sin α/b = 1, ∴ asinα+bcosα = AB.

∴ (√ A 2+B 2) * SIN (α+φ) = AB, and the square arrangement of both sides can get1/A2+1/B2 =1/sin (α+φ) 2.

∫sin(α+φ) is between-1 and 1, which is not equal to 0; ∴ 1/sin (α+φ) 2 is greater than or equal to 1, that is, 1/A 2+ 1/.