better lone parenthesis handling

Author: GabrielMahan

lib/Symbols.js

@@ -39,6 +39,10 @@ Symbols.getLastSymbolTerm = function(node, symbolName) {
       }
     }
   }
+  else if (Node.Type.isParenthesis(node)) {
+    return Symbols.getLastSymbolTerm(node.content, symbolName);
+  }
+
   return null;
 };
 

lib/solveEquation/EquationOperations.js

@@ -128,10 +128,16 @@ EquationOperations.removeSymbolFromRightSide = function(equation, symbolName) {
 // or dividing all other symbols and constants from both sides appropriately
 // TODO: support inverting functions e.g. sqrt, ^, log etc.
 EquationOperations.isolateSymbolOnLeftSide = function(equation, symbolName) {
-  const leftNode = equation.leftNode;
-  let nonSymbolTerm = Symbols.getLastNonSymbolTerm(leftNode, symbolName);
+  let leftNode = equation.leftNode;
+
+  if (Node.Type.isParenthesis(leftNode)) {
+    // if entire left node is a parenthesis, we can ignore the parenthesis
+    leftNode = leftNode.content;
+  }
 
+  let nonSymbolTerm = Symbols.getLastNonSymbolTerm(leftNode, symbolName);
   let inverseOp, inverseTerm, changeType;
+
   if (!nonSymbolTerm) {
     return EquationStatus.noChange(equation);
   }

test/solveEquation/solveEquation.test.js

@@ -95,6 +95,8 @@ describe('solveEquation for =', function () {
     ['2/(1 + 1 + 4x) = 1/3', 'x = 1'],
     ['(3 + x) / (x^2 + 3) = 1', 'x = [0, 1]'],
     ['6/x + 8/(2x) = 10', 'x = 1'],
+    ['(x+1)=4', 'x = 3'],
+    ['((x)/(4))=4', 'x = 16']
     // TODO: fix these cases, fail because lack of factoring support, for complex #s,
     // for taking the sqrt of both sides, etc
     // ['(x + y) (y + 2) = 0', 'y = -y'],