In multiplying rational expressions, we multiply the
numerators and denominators, then express the product in its
lowest term.
The product of rational expressions
𝑎
𝑏
and
𝑐
𝑑
, where a, b, c, and
d are polynomials and b ≠ 0 and d ≠ 0 is given by
𝑎
𝑏
.
𝑐
𝑑
=
𝑎𝑐
𝑏𝑑
.
Example 1.
𝟐
𝟑
.
𝟏
𝟒
Example 2.
𝟏𝟓
𝟐𝒚𝟐 .
𝒚𝟒
𝟐𝟎
=
(2)(1)
(3)(4)
=
2
12
(2) =
𝟏
𝟔
Or use cross-cancellation
=
2
3
.
1
4
=
1
2
3
.
1
4 2
=
(1)(1)
(3)(2)
=
𝟏
𝟔
=
𝟏𝟓
𝟐𝒚𝟐 .
𝒚𝟒
𝟐𝟎
=
15𝑦4
40𝑦2(5y2) =
𝟑𝒚𝟐
𝟖
By cross-cancellation
=
15
2𝑦2 .
𝑦4
20
=
𝟑
15
𝟐 2𝑦2 .
𝑦4 𝒚𝟐
20 𝟒
=
𝟑𝒚𝟐
𝟖
Example 3.
𝟒𝒂𝟐
𝒃
𝒄𝟑 .
𝟑𝒄𝟓
𝟖𝒂𝟑
𝒃
Example 4.
𝒙𝟐
− 𝟒
𝟐𝒙
.
𝟖𝒙𝟐
𝒙+𝟐
=
𝟒𝒂𝟐
𝒃
𝒄𝟑 .
𝟑𝒄𝟓
𝟖𝒂𝟑
𝒃
=
12𝑎2
𝑏𝑐5
8𝑎3
𝑏𝑐3 (4a2bc3) =
𝟑𝒄𝟐
𝟐𝒂
Cross-multiplication
=
4𝑎2
𝑏
𝑐3 .
3𝑐5
8𝑎3
𝑏
=
𝟏
4𝑎2
𝑏
𝑐3 .
3𝑐5 𝒄𝟐
8𝑎3
𝑏 𝟐𝒂
=
(1)(3)(𝑐2
)
2𝑎
=
𝟑𝒄𝟐
𝟐𝒂
=
𝑥2
− 4
2𝑥
.
8𝑥2
𝑥+2
=
(𝑥+2)(𝑥 −2)
2𝑥
.
(2𝑥)(4𝑥)
1(𝑥+2)
=
(𝑥 −2)(4𝑥)
1
= (x – 2)(4x)
Example 5.
𝟐𝒙 −𝟔
𝟑𝒙
.
𝒙
𝒙 −𝟑
Example 6.
𝒙+𝟓
𝟒𝒙
.
𝟏𝟐𝒙𝟐
𝒙𝟐
+𝟕𝒙+𝟏𝟎
=
2𝑥 −6
3𝑥
.
𝑥
𝑥 −3
=
2 (𝑥 −3)
3𝑥
.
𝑥
1(𝑥 −3)
=
2
(3)(1)
=
𝟐
𝟑
=
𝒙+𝟓
𝟒𝒙
.
𝟏𝟐𝒙𝟐
𝒙𝟐
+𝟕𝒙+𝟏𝟎
=
1(𝑥+5)
4𝑥
.
(4𝑥)(3𝑥)
(𝑥+5)(𝑥+2)
=
(1)(3𝑥)
(𝑥+2)
=
𝟑𝒙
𝒙+𝟐
Multiplication of rational expression

Multiplication of rational expression

  • 2.
    In multiplying rationalexpressions, we multiply the numerators and denominators, then express the product in its lowest term. The product of rational expressions 𝑎 𝑏 and 𝑐 𝑑 , where a, b, c, and d are polynomials and b ≠ 0 and d ≠ 0 is given by 𝑎 𝑏 . 𝑐 𝑑 = 𝑎𝑐 𝑏𝑑 .
  • 3.
    Example 1. 𝟐 𝟑 . 𝟏 𝟒 Example 2. 𝟏𝟓 𝟐𝒚𝟐. 𝒚𝟒 𝟐𝟎 = (2)(1) (3)(4) = 2 12 (2) = 𝟏 𝟔 Or use cross-cancellation = 2 3 . 1 4 = 1 2 3 . 1 4 2 = (1)(1) (3)(2) = 𝟏 𝟔 = 𝟏𝟓 𝟐𝒚𝟐 . 𝒚𝟒 𝟐𝟎 = 15𝑦4 40𝑦2(5y2) = 𝟑𝒚𝟐 𝟖 By cross-cancellation = 15 2𝑦2 . 𝑦4 20 = 𝟑 15 𝟐 2𝑦2 . 𝑦4 𝒚𝟐 20 𝟒 = 𝟑𝒚𝟐 𝟖
  • 4.
    Example 3. 𝟒𝒂𝟐 𝒃 𝒄𝟑 . 𝟑𝒄𝟓 𝟖𝒂𝟑 𝒃 Example4. 𝒙𝟐 − 𝟒 𝟐𝒙 . 𝟖𝒙𝟐 𝒙+𝟐 = 𝟒𝒂𝟐 𝒃 𝒄𝟑 . 𝟑𝒄𝟓 𝟖𝒂𝟑 𝒃 = 12𝑎2 𝑏𝑐5 8𝑎3 𝑏𝑐3 (4a2bc3) = 𝟑𝒄𝟐 𝟐𝒂 Cross-multiplication = 4𝑎2 𝑏 𝑐3 . 3𝑐5 8𝑎3 𝑏 = 𝟏 4𝑎2 𝑏 𝑐3 . 3𝑐5 𝒄𝟐 8𝑎3 𝑏 𝟐𝒂 = (1)(3)(𝑐2 ) 2𝑎 = 𝟑𝒄𝟐 𝟐𝒂 = 𝑥2 − 4 2𝑥 . 8𝑥2 𝑥+2 = (𝑥+2)(𝑥 −2) 2𝑥 . (2𝑥)(4𝑥) 1(𝑥+2) = (𝑥 −2)(4𝑥) 1 = (x – 2)(4x)
  • 5.
    Example 5. 𝟐𝒙 −𝟔 𝟑𝒙 . 𝒙 𝒙−𝟑 Example 6. 𝒙+𝟓 𝟒𝒙 . 𝟏𝟐𝒙𝟐 𝒙𝟐 +𝟕𝒙+𝟏𝟎 = 2𝑥 −6 3𝑥 . 𝑥 𝑥 −3 = 2 (𝑥 −3) 3𝑥 . 𝑥 1(𝑥 −3) = 2 (3)(1) = 𝟐 𝟑 = 𝒙+𝟓 𝟒𝒙 . 𝟏𝟐𝒙𝟐 𝒙𝟐 +𝟕𝒙+𝟏𝟎 = 1(𝑥+5) 4𝑥 . (4𝑥)(3𝑥) (𝑥+5)(𝑥+2) = (1)(3𝑥) (𝑥+2) = 𝟑𝒙 𝒙+𝟐