Question

in a triangle 1/a+c + 1/b+c = 3/a+b+c show that angle c=60degree

Answer 1

I assume you are working with an equilateral triangle.  

b = 60 degrees. Given

a = 60 degrees The angles in an equilateral tringle are equal.

c = 60 degrees The angles in an equilateral triangle are equal.

1/b + c = 1/120 addition

1/a + c = 1/120 addition  

1/120 + 1/120 = 2/120 = 1/60 addition, reduction.  

3/a + b + c = 3/180 substitution  

3/180 = 1/60 Reduction.

They are the same, 1/60.

Cleomenius.