prove that AB is tangent to circle

Answer:
See Explanation
Step-by-step explanation:
[tex] AB^2 +OB^2 = 4^2 +3^2 = 16 + 9 =25[/tex]
.....(1)
[tex] OA^2 = 5^2 = 25[/tex]
..... (2)
From equations (1) & (2)
[tex] AB^2 +OB^2 = OA^2[/tex]
Therefore, by converse of Pythagoras theorem, triangle ABO is right angled triangle right angle at B.
Therefore,
Radius OB is perpendicular to AB.
Hence, AB is tangent to the circle with center O at point B.