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Why can k(k+1)+2(k+1)k(k+1) + 2(k+1) be rewritten as (k+1k+1)(k+2k+2)?

This rewrite is possible due to the distributive property of multiplication over addition, specifically factoring out the common term (k+1k+1). Both terms in the sum k(k+1)k(k+1) and 2(k+1)2(k+1) share the factor (k+1k+1). Extracting this common factor leaves (k+2k + 2) inside the parentheses.

Conditions

  • The expression is a sum of two terms: k(k+1)k(k+1) and 2(k+1)2(k+1).
  • (k+1k+1) is a common factor in both terms.

Reasoning, step by step

  1. Identify the common factor (k+1k+1) in both terms.
  2. Apply the factoring rule: ab + ac = a(b+c)a(b+c).
  3. Let a=(k+1)a = (k+1), b=kb = k, and c=2c = 2.
  4. Rewrite the expression as (k+1k+1)(k+2k+2).
  5. Verify by expanding: (k+1k+1)(k+2k+2) = k2+2k+k+2=k2+3k+2k^2 + 2k + k + 2 = k^2 + 3k + 2, which matches k(k+1)+2(k+1)=k2+k+2k+2=k2+3k+2k(k+1) + 2(k+1) = k^2 + k + 2k + 2 = k^2 + 3k + 2.

Example

The video shows the step: 'k(k+1)+2(k+1)=(k+1)(k+2)k(k+1) + 2(k+1) = (k+1)(k+2)'. The narrator explains, 'Because (k+1k+1) is common to both terms, factor it out to obtain (k+1k+1)(k+2k+2).'

Common misconceptions

  • Thinking that the terms cannot be combined because they are different.
  • Incorrectly factoring out only k or only 1.

Watch the explanation

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Answers are generated from source material and independently checked. Consult the original video or creator if something is unclear.