Finding the Unknown
Part of the Fundamentals section of Coddy's Algebra journey. Lesson 2 of 64.
One way to find a solution is to try numbers. Take x + 3 = 8. Try 4: 4 + 3 is 7, which is too small. Try 6: 6 + 3 is 9, which is too big. Try 5: both sides are 8. So x = 5.
This method is called guess and check. You try a value and see whether it makes the equation true. The equation x + 3 = 8 has only one solution. When x gets bigger, the left side gets bigger too, and it equals 8 only when x = 5.
Guess and check can take many tries. Equations such as 7x - 4 = 3x + 8 or x/2 + x/3 = 10 are hard to solve this way. It is even harder when the solution is a fraction or a negative number. In the next lessons you will learn steps that find the unknown without guessing. In this lesson, find the solution by trying values.
Challenge
EasyWhich number makes x + 6 = 10 true?
Try a few numbers, then write the one that works: x = ...
Try it yourself
Solve for x
Test yourselfThis lesson includes a short quiz. Start the lesson to answer it and track your progress.
All lessons in Fundamentals
1What an Equation Is
The EquationFinding the UnknownThe Same to Both SidesSolved Means AloneRecap: First Equations4Two-Step Equations
Two Layers to UndoSubtract, Then DivideAdd, Then DivideA Division InsideNegatives in Two StepsRecap: Two-Step Equations2One-Step Equations
Undoing AdditionUndoing SubtractionUndoing MultiplicationUndoing DivisionInverse OperationsRecap: One-Step Equations5Tidying First
Like TermsTerms and Numbers MixedThe Distributive PropertyDistributing a SubtractionTidy, Then SolveRecap: Tidying First