If A=B+C and the magnitude of A,B.C are 5,4,3 units then angle between A and C is ?

Answer 1

To avoid confusion, the sides of the
triangle should use lower case letters:

A = B+C
a = 5
b = 4
c = 3

Angle between a and c = ?

We have a 3-4-5 rt. triangle.
A = B+C = 90o

The longest side is always opposite the
largest angle:
a = hyp. = 5 Units.
b = 4 Units.
c = 3 Units.

Tan B = b/c = 4/3 = 1.33333
B = 53.13o = Angle between a and c.