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Add support for second variable canceling out #254

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Add support for second variable canceling out #254

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10 changes: 7 additions & 3 deletions lib/solveEquation/stepThrough.js
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Original file line number Diff line number Diff line change
Expand Up @@ -42,8 +42,7 @@ function stepThrough(leftNode, rightNode, comparator, debug=false) {
if (symbolSet.size === 0) {
return solveConstantEquation(equation, debug);
}
const symbolName = symbolSet.values().next().value;

let symbolName = symbolSet.values().next().value;
let equationStatus;
let steps = [];

Expand Down Expand Up @@ -80,8 +79,13 @@ function stepThrough(leftNode, rightNode, comparator, debug=false) {
equation.rightNode = flattenOperands(equation.rightNode);

// at this point, the symbols might have cancelled out.
if (Symbols.getSymbolsInEquation(equation).size === 0) {
const postSimplificationSymbols = Symbols.getSymbolsInEquation(equation)
if (postSimplificationSymbols.size === 0) {
// if all symbols are canceled out, the equation can now be treated as a constant equation
return solveConstantEquation(equation, debug, steps);
} else if (!postSimplificationSymbols.has(symbolName)) {
// if the original symbol is canceled out but other sybols remain, reset the target symbol
symbolName = postSimplificationSymbols.values().next().value;
}

// The left side of the equation is either factored or simplified.
Expand Down
5 changes: 4 additions & 1 deletion test/solveEquation/solveEquation.test.js
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Expand Up @@ -96,7 +96,9 @@ describe('solveEquation for =', function () {
['(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']
['((x)/(4))=4', 'x = 16'],
['x+y=x+y', '0 = 0'],
['y + 2x = 14 + y', 'x = 7']
// 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'],
Expand Down Expand Up @@ -155,6 +157,7 @@ describe('constant comparison support', function () {
['1 <= 1', ChangeTypes.STATEMENT_IS_TRUE],
['2 <= 1', ChangeTypes.STATEMENT_IS_FALSE],
['1 <= 2', ChangeTypes.STATEMENT_IS_TRUE],
['0 = 0', ChangeTypes.STATEMENT_IS_TRUE],
['( 1) = ( 14)', ChangeTypes.STATEMENT_IS_FALSE],
// TODO: when we support fancy exponent and sqrt things
// ['(1/64)^(-5/6) = 32', ChangeTypes.STATEMENT_IS_TRUE],
Expand Down