Learn how to solve L.C.M. of polynomials by factorization splitting the middle term.
Solved examples on lowest common multiple of polynomials by factorization:
1. Find the L.C.M of m^{3} – 3m^{2} + 2m and m^{3} + m^{2} – 6m by factorization.= m[m(m - 2) - 1(m - 2)]
= m(m - 2) (m - 1)
= m × (m - 2) × (m - 1)
= m[m(m + 3) - 2(m + 3)]
= m(m + 3)(m - 2)
= m × (m + 3) × (m - 2)
In both the expressions, the common factors are ‘m’ and ‘(m - 2)’; the extra common factors are (m - 1) in the first expression and (m + 3) in the 2nd expression.
Therefore, the required L.C.M. = m × (m - 2) × (m - 1) × (m + 3)
= m(m - 1) (m - 2) (m + 3)
= 3a[a(a - 3x) - 3x(a - 3x)]
= 3a(a - 3x) (a - 3x)
= 3 × a × (a - 3x) × (a - 3x)
= 2 × 3 × a × a × (a + 3x) × (a - 3x)
The common factors of the above three expressions is ‘a’ and other common factors of first and third expressions are ‘3’ and ‘(a - 3x)’.
The common factors of second and third expressions are ‘2’, ‘a’ and ‘(a + 3x)’.
Other than these, the extra common factors in the first expression is ‘(a - 3x)’ and in the second expression are ‘2’ and ‘(a + 3x)’
Therefore, the required L.C.M. = a × 3 × (a - 3x) × 2 × a × (a + 3x) × (a - 3x) × 2 × (a + 3x) = 12a^{2}(a + 3x)^{2}(a - 3x)^{2}More problems on L.C.M. of polynomials by factorization splitting the middle term:
3. Find the L.C.M. of 4(a^{2} - 4), 6(a^{2} - a - 2) and 12(a^{2} + 3a - 10) by factorization.= 6[a(a - 2) + 1(a - 2)]
= 6(a - 2) (a + 1)
= 2 × 3 × (a - 2) × (a + 1)
Third expression = 12(a^{2} + 3a - 10)= 12[a(a + 5) - 2(a + 5)]
= 12(a + 5) (a - 2)
= 2 × 2 × 3 × (a + 5) × (a - 2)
In the above three expressions the common factors are 2 and (a - 2).
Only in the second expression and third expression the common factor is 3.
Other than these, the extra common factors are (a + 2) in the first expression, (a + 1) in the second expression and 2, (a + 5) in the third expression.
Therefore, the required L.C.M. = 2 × (a - 2) × 3 × (a + 2) × (a + 1) × 2 × (a + 5)
= 12(a + 1) (a + 2) (a - 2) (a + 5)
8th Grade Math Practice
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