2a-b=ab+3 solve for a
All you have to do is remember that it is an equation.
That means, whatever you do to the lhs, yoou must also do to the rhs, to keep it equal,
Your equation is,
2a - b = ab + 3 (subract ab from both sides)
2a - b - ab = ab + 3 - ab (cancel out the ab's on the rhs)
2a - b - ab = 3 ( rearrange the lhs)
2a - ab - b = 3 (add b to both sides)
2a - ab - b + b = 3 + b (cancel out the b's on the lhs)
2a - ab = 3 + b (take out a as a common factor, on the lhs)
a(2 - b) = 3 + b (now divide both sides by (2 - b))
a = (3 + b)/(2 - b)