Could it get any more complicated than this?

Calculus Level 5

a [ ( 2 + 4 + x ) b b c ( 2 + 4 + x ) d d + e ( 2 + 4 + x ) f f ] a \left [ \frac { \left ( \sqrt{2 + \sqrt{4+ \sqrt x }} \right )^b }{b} - \frac {c \left ( \sqrt{2 + \sqrt{4+ \sqrt x }} \right )^d }{d} + \frac {e \left ( \sqrt{2 + \sqrt{4+ \sqrt x }} \right )^f }{f} \right ]

Ignoring the arbitrary constant, the antiderivative of function 2 + 4 + x \sqrt{2 + \sqrt{4+ \sqrt x }} can be written as the expression given above for positive integers a , b , c , d , e , f a,b,c,d,e,f with gcd ( c , d ) = gcd ( e , f ) = 1 \text{gcd}(c,d) = \text{gcd}(e,f) = 1 .

What is the value of a + b + c + d + e + f a+b+c+d+e+f ?

Try solving One Two Three Four Five Present!


The answer is 43.

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1 solution

Anupam Khandelwal
Mar 29, 2015

2 + 4 + x . d x L e t 2 + 4 + x = t t 2 2 = 4 + x ( ( t 2 2 ) 2 4 ) 2 = x x = ( t 4 4 t 2 ) 2 d x = 2 ( t 4 4 t 2 ) ( 4 t 3 8 t ) . d t N o w t h e i n t e g r a l b e c o m e s 2 t ( t 4 4 t 2 ) ( 4 t 3 8 t ) . d t 8 ( t 8 6 t 6 + 8 t 4 ) d t 8 [ 2 + 4 + x 9 9 6 2 + 4 + x 7 7 + 8 2 + 4 + x 5 5 ] + k B y t h i s w e g e t a + b + c + d + e + f = 8 + 9 + 6 + 7 + 8 + 5 = 43 \int { \sqrt { 2+\sqrt { 4+\sqrt { x } } } .dx } \\ \\ Let\quad \sqrt { 2+\sqrt { 4+\sqrt { x } } } =\quad t\\ \\ { t }^{ 2 }\quad -\quad 2\quad =\quad \sqrt { 4+\sqrt { x } } \\ ({ { { (t }^{ 2 }-2) }^{ 2 } }-4)^{ 2 }\quad =\quad x\\ \\ x\quad =\quad { ({ t }^{ 4 }-4{ t }^{ 2 }) }^{ 2 }\\ dx\quad =\quad 2({ t }^{ 4 }-{ 4t }^{ 2 })(4{ t }^{ 3 }-8{ t }).dt\\ \\ Now\quad the\quad integral\quad becomes\\ \\ \int { 2t({ t }^{ 4 }{ -4t }^{ 2 }) } ({ 4t }^{ 3 }{ -8t }).dt\\ 8\int { ({ t }^{ 8 }{ -6t }^{ 6 }{ +8t }^{ 4 }) } dt\\ 8\left[ \frac { { \sqrt { 2+\sqrt { 4+\sqrt { x } } } }^{ 9 } }{ 9 } \quad -\quad \frac { { 6\sqrt { 2+\sqrt { 4+\sqrt { x } } } }^{ 7 } }{ 7 } \quad +\quad \frac { { 8\sqrt { 2+\sqrt { 4+\sqrt { x } } } }^{ 5 } }{ 5 } \right] \quad +\quad k\\ \\ By\quad this\quad we\quad get\quad a+b+c+d+e+f=8+9+6+7+8+5\\ \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad =\quad 43\\

hey is this problem really of level 5 !!!! ?

Rishabh Jain - 6 years, 2 months ago

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Well I can't do anything about its level .

Anupam Khandelwal - 6 years, 2 months ago

I think this is one of those problems that just looks hard, but really isn't.

Milly Choochoo - 5 years ago

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