If ∫ x ( x − 1 ) 3 d x = b a x 2 7 − e d x 2 5 + u x 2 3 + v x 2 1 + C
where C is any constant and the pairs ( a , b ) and ( d , e ) are pairs of co-prime positive integers. Then find the value a + b + d + e + u + v
Clarification: -Rational no.s b a and e d are in the standard form.
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I = ∫ x ( x − 1 ) 3 d x = ∫ u ( u 2 − 1 ) 3 ⋅ 2 u d u = 2 ∫ ( u 6 − 3 u 4 + 3 u 2 − 1 ) d u = 7 2 u 7 − 5 6 u 5 + 2 u 3 − 2 u + C = 7 2 x 2 7 − 5 6 x 2 5 + 2 x 2 3 − 2 x 2 1 + C Let u 2 = x ⟹ 2 u d u = d x where C is the constant of integration. Putting back u = x
Therefore, a + b + d + e + u + v = 2 + 7 + 6 + 5 + 2 − 2 = 2 0 .
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∫ x ( x − 1 ) 3 d x = ∫ x ( x − 1 ) 3 d x = ∫ { x 1 / 2 x 3 − 3 x 2 + 3 x − 1 d x
⇒ ∫ x ( x − 1 ) 3 d x = ∫ ( x 5 / 2 − 3 x 3 / 2 + 3 x 1 / 2 − x − 1 / 2 ) d x = 7 2 x 7 / 2 − 5 6 x 5 / 2 + 2 x 3 / 2 − 2 x 1 / 2
⇒ a = 2 , b = 7 , d = 6 , e = 5 , u = 2 , v = − 2 ⇒ a + b + d + e + u + v = 2 + 7 + 6 + 5 + 2 − 2 = 2 0