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Algebra basics
Letters stand for numbers
In algebra a letter is a number we do not know yet. 3n means 3 lots of n. Everything you already know about arithmetic still applies.
Keeping an equation balanced
An equation is a balance. Whatever you do to one side you must do to the other. Undo the additions and subtractions first, then undo the multiplications and divisions.
Collecting like terms
Only terms with exactly the same letter part can be added together. 4a + 3a = 7a, but 4a + 3b cannot be simplified any further.
Worked example
Solve 4x + 5 = 21.
- 1First check what's being asked: the value of one x.
- 2Undo the +5 by subtracting 5 from both sides: 4x = 16.
- 3Undo the x4 by dividing both sides by 4: x = 4.
- 4Check by substituting back: 4 x 4 + 5 = 21. Correct.
Answer: x = 4