(b - c)/b * (b+c)/b Notice how the second fraction is inverted and multiplied. That's how you handle a 4 tier fraction. Here's a simpler example
What you get with your problem is
(b^2 - c^2)/b^2
it is contrapositive
i could not see the question too well so check yourself again too . this is because i want you to get it correct.
it have 5 sides and 5 identicle angle.the rest does not have the same property as b.
(( b - c )/ b ) + (b / ( b + c ))...