The given equation is sina + tga = 1 + cosa.

To solve for tga, we can use the Pythagorean identity sin^2(a) + cos^2(a) = 1.

Since sina = sin(a) and cosa = cos(a), we have:

sin^2(a) + cos^2(a) = 1
(sin(a))^2 + (cos(a))^2 = 1
sina^2 + cosa^2 = 1

Substitute the values into the given equation:

tga = 1 + cosa - sina
tga = 1 + cosa - sqrt(1 - (cosa)^2)
tga = 1 + cosa - sqrt(1 - (cosa)^2)

Therefore, the value of tga is 1 + cosa - sqrt(1 - (cosa)^2).