In algebra, a number can serve as a coefficient or an exponent.
a) Explain the difference between \(4x\) and \(x^4\) by writing \(4x\) as repeated addition and \(x^4\) as repeated multiplication.
b) Use repeated addition, without coefficients, to show that \(2a+3a=5a\).
c) Use repeated addition to explain why \(3x+2y\) cannot be combined into one term such as \(5xy\).
Hints
- A coefficient tells how many copies are added; an exponent tells how many equal factors are multiplied.
- Expand each coefficient into repeated addition.
- Can terms with different variable parts be counted as copies of the same quantity?
- Count the total number of \(a\)-terms in part b).
Solution
1. The coefficient \(4\) in \(4x\) counts four addends: \(x+x+x+x\). The exponent \(4\) in \(x^4\) counts four factors: \(x\times x\times x\times x\).
2. Write \(2a+3a\) as \((a+a)+(a+a+a)\). This is \(a+a+a+a+a=5a\).
3. Write \(3x+2y\) as \(x+x+x+y+y\). The \(x\)-terms and \(y\)-terms are unlike terms, so they cannot be combined into a single term.
Answer
a) \(4x=x+x+x+x\), while \(x^4=x\times x\times x\times x\).
b) \(2a+3a=(a+a)+(a+a+a)=a+a+a+a+a=5a\).
c) \(3x+2y=x+x+x+y+y\). Since \(x\) and \(y\) are different variables, the terms are not like terms and cannot be combined.