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Collecting like terms

Collecting like terms

The expression 4x+3+2x−1\displaystyle 4x+3+2x-1 has four terms: 4x\displaystyle 4x, 3\displaystyle 3, 2x\displaystyle 2x and −1\displaystyle -1. A term is a number, a variable or a product of them, and the sign before it belongs to it: the last term is −1\displaystyle -1, not 1\displaystyle 1.

Like terms
The number before the variable is called the coefficient: in −5x\displaystyle -5x the coefficient is −5\displaystyle -5, and in x\displaystyle x it is 1.

Like terms have the same letter part: 4x\displaystyle 4x and 2x\displaystyle 2x are like terms, and so are 3\displaystyle 3 and −1\displaystyle -1 (two numbers). x\displaystyle x and x2\displaystyle x^2 are not like terms, and neither are a\displaystyle a and b\displaystyle b.

Collecting like terms

Like terms can be added into one term: 4x+2x=6x\displaystyle {4x+2x}={6x}, because 4 times x\displaystyle x plus 2 times x\displaystyle x is 6 times x\displaystyle x. This is collecting like terms: add the coefficients, and the letter part stays as it is. So 4x+3+2x−1=6x+2\displaystyle {4x+3+2x-1}={6x+2}. Terms that are not alike cannot be collected: 6x+2\displaystyle 6x+2 stays 6x+2\displaystyle 6x+2.

Like terms with signed coefficients
x−x=0\displaystyle {x-x}={0}: opposite terms cancel each other.

The coefficients are signed numbers, and they are added as we learned: 5y−8y=−3y\displaystyle {5y-8y}={-3y}; −3x+7−5x−2=−8x+5\displaystyle {-3x+7-5x-2}={-8x+5}; 2a+3b−a+4b=a+7b\displaystyle {2a+3b-a+4b}={a+7b}.

Exercise 1

Collect like terms.

a

    / – fraction bar · Tab or the arrows – between numerator and denominator, then a note above or below · Enter – check and a new line · * – times · ^ – power, ↓ – end of the power

    / – fraction bar · Tab or the arrows – between numerator and denominator, then a note above or below · Enter – a new line · * – times · ^ – power, ↓ – end of the power

    b

      / – fraction bar · Tab or the arrows – between numerator and denominator, then a note above or below · Enter – check and a new line · * – times · ^ – power, ↓ – end of the power

      / – fraction bar · Tab or the arrows – between numerator and denominator, then a note above or below · Enter – a new line · * – times · ^ – power, ↓ – end of the power

      c

        / – fraction bar · Tab or the arrows – between numerator and denominator, then a note above or below · Enter – check and a new line · * – times · ^ – power, ↓ – end of the power

        / – fraction bar · Tab or the arrows – between numerator and denominator, then a note above or below · Enter – a new line · * – times · ^ – power, ↓ – end of the power

        d

          / – fraction bar · Tab or the arrows – between numerator and denominator, then a note above or below · Enter – check and a new line · * – times · ^ – power, ↓ – end of the power

          / – fraction bar · Tab or the arrows – between numerator and denominator, then a note above or below · Enter – a new line · * – times · ^ – power, ↓ – end of the power

          e

            / – fraction bar · Tab or the arrows – between numerator and denominator, then a note above or below · Enter – check and a new line · * – times · ^ – power, ↓ – end of the power

            / – fraction bar · Tab or the arrows – between numerator and denominator, then a note above or below · Enter – a new line · * – times · ^ – power, ↓ – end of the power

            f

              / – fraction bar · Tab or the arrows – between numerator and denominator, then a note above or below · Enter – check and a new line · * – times · ^ – power, ↓ – end of the power

              / – fraction bar · Tab or the arrows – between numerator and denominator, then a note above or below · Enter – a new line · * – times · ^ – power, ↓ – end of the power

              A term times a number

              4⋅3x\displaystyle 4\cdot3x is 4⋅3⋅x=12x\displaystyle {4\cdot3\cdot x}={12x}. Like collecting like terms, this is simplifying: writing a shorter equivalent expression. Multiply the numbers, and the variable stays. More examples: 2a⋅5=10a\displaystyle {2a\cdot5}={10a}; −3⋅4y=−12y\displaystyle {-3\cdot4y}={-12y}; x⋅2x=2x2\displaystyle {x\cdot2x}={2x^2}.

              Exercise 2

              Simplify.

              a

                / – fraction bar · Tab or the arrows – between numerator and denominator, then a note above or below · Enter – check and a new line · * – times · ^ – power, ↓ – end of the power

                / – fraction bar · Tab or the arrows – between numerator and denominator, then a note above or below · Enter – a new line · * – times · ^ – power, ↓ – end of the power

                b

                  / – fraction bar · Tab or the arrows – between numerator and denominator, then a note above or below · Enter – check and a new line · * – times · ^ – power, ↓ – end of the power

                  / – fraction bar · Tab or the arrows – between numerator and denominator, then a note above or below · Enter – a new line · * – times · ^ – power, ↓ – end of the power

                  c

                    / – fraction bar · Tab or the arrows – between numerator and denominator, then a note above or below · Enter – check and a new line · * – times · ^ – power, ↓ – end of the power

                    / – fraction bar · Tab or the arrows – between numerator and denominator, then a note above or below · Enter – a new line · * – times · ^ – power, ↓ – end of the power

                    d

                      / – fraction bar · Tab or the arrows – between numerator and denominator, then a note above or below · Enter – check and a new line · * – times · ^ – power, ↓ – end of the power

                      / – fraction bar · Tab or the arrows – between numerator and denominator, then a note above or below · Enter – a new line · * – times · ^ – power, ↓ – end of the power

                      Exercise 3

                      A rectangle is 3a\displaystyle 3a long and a\displaystyle a wide.
                      Write an expression for its perimeter and simplify it.