A1+a2+a3=180 solve for a1
Answer: a1=180-a2-a3....
A1 = 180 - (a2 + a3) ;_______________________or: _______________________A1 = 180 - a2 - a3._______________________.Since there are no values given, we solve for "A1" by isolating "A1" and solving in terms of the remaining values.