Question

How to solve it ?......

Answer 1

Pythagorean theorem in triangle OAB

then find the AB.

AB=5. cm

then in triangle CAB

BC^2=AB^2+AC^2

so triangle CABis right angle triangle

Answer 2

$oa ^{2} + ob {}^{2} = ab {}^{2}$
from this you will get the value of AB
now use Pythagoras theorem for triangle CAB assuming angle A as right angle if the left hand side is equal to right hand side then the angle CAB is 90degree