Solution to definite integration by substitution different when pulling out a constant (C4 Edexcel June 2013 Q5(b))

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The solution to definite integration appears to be different when pulling out a constant. I am not sure why. Can anyone explain? (Integration by Substitution : Core Maths : C4 Edexcel June 2013 Q5(b))

Integration by Substitution : Core Maths : C4 Edexcel June 2013 Q5(a) : ExamSolutions

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