The Critical Points

Calculus Level pending

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The answer is 51.

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1 solution

Luis Tabule
Dec 6, 2014

T h i s i s t h e s o l u t i o n I u s e d i n s o l v i n g t h e m a t h p r o b l e m . f ( x ) = x 2 4 x 1 f ( x ) = 2 x 4 0 = 2 x 4 2 x = 4 x = 2 U s i n g x = 2 : f ( 2 ) = 4 8 1 f ( 2 ) = 5 T h e c r i t i c a l p o i n t o f f ( x ) i s ( 2 , 5 ) . g ( x ) = x 3 9 x 2 + 15 x 5 g ( x ) = 3 x 2 18 x + 15 0 = ( 3 x 3 ) ( x 5 ) x = 1 , x = 5 U s i n g x = 1 : g ( 1 ) = 1 9 + 15 5 g ( 1 ) = 2 U s i n g x = 5 g ( 5 ) = 125 225 + 75 5 g ( 5 ) = 30 T h e c r i t i c a l p o i n t s o f g ( x ) a r e ( 1 , 2 ) a n d ( 5 , 30 ) . S i n c e A i s t h e s u m o f a l l x c o o r d i n a t e s o f t h e c r i t i c a l p o i n t s o f f ( x ) a n d g ( x ) , t h e n : A = 2 + 1 + 5 A = 8 S i n c e B i s t h e s u m o f a l l y c o o r d i n a t e s o f t h e c r i t i c a l p o i n t s o f f ( x ) a n d g ( x ) , t h e n : B = 5 + 2 30 B = 33 F o r t h e z e r o e s o f h ( x ) : h ( x ) = A x 2 2 ( B 3 ) x ( B + 1 ) h ( x ) = 4 x 2 + 36 x + 32 0 = 4 x 2 + 36 x + 32 0 = ( 4 x + 4 ) ( x + 8 ) x = { 1 , 8 } S i n c e t h e z e r o e s o f j ( x ) a r e t h e d o u b l e o f t h e z e r o e s o f h ( x ) , t h e n 2 a n d 16 a r e t h e z e r o e s o f j ( x ) . L e t : r 1 = 2 a n d r 2 = 16 j ( x ) = ( x r 1 ) ( x r 2 ) j ( x ) = ( x + 2 ) ( x + 16 ) j ( x ) = x 2 + 18 x + 32 , w h e r e a = 1 , b = 18 , a n d c = 32. F o r a + b + c : a + b + c = 1 + 18 + 32 a + b + c = 51 C o n j e c t u r e : T h e s u m o f a + b + c o f t h e s t a n d a r d f o r m o f j ( x ) i s 51. / / This\quad is\quad the\quad solution\quad I\quad used\quad in\quad solving\quad the\quad math\quad problem.\\ f\left( x \right) ={ \quad x }^{ 2 }-4x-1\\ f^{ \quad \prime }\left( x \right) =\quad 2x-4\\ 0=\quad 2x-4\\ 2x=4\\ x=2\\ \\ Using\quad x=2:\\ f(2)=\quad 4-8-1\\ f(2)=\quad -5\\ The\quad critical\quad point\quad of\quad f(x)\quad is\quad (2,-5).\\ \\ g(x)\quad =\quad { x }^{ 3 }-{ 9x }^{ 2 }+15x-5\\ g^{ \prime }\left( x \right) =\quad 3{ x }^{ 2 }-18x+15\\ 0=\quad (3x-3)(x-5)\\ x=1,\quad x=5\\ Using\quad x=1:\\ g(1)\quad =\quad 1-9+15-5\\ g(1)\quad =\quad 2\\ Using\quad x=5\\ g(5)\quad =\quad 125-225+75-5\\ g(5)\quad =\quad -30\\ The\quad critical\quad points\quad of\quad g(x)\quad are\quad (1,2)\quad and\quad (5,-30).\\ \\ Since\quad A\quad is\quad the\quad sum\quad of\quad all\quad x-coordinates\quad of\quad the\quad critical\quad points\quad of\quad f(x)\quad and\quad g(x),\quad \\ then:\\ A=2+1+5\\ A=\quad 8\\ Since\quad B\quad is\quad the\quad sum\quad of\quad all\quad y-coordinates\quad of\quad the\quad critical\quad points\quad of\quad f(x)\quad and\quad g(x),\\ then:\\ B=\quad -5+2-30\\ B=\quad -33\\ \\ For\quad the\quad zeroes\quad of\quad h(x):\\ h(x)=\frac { A{ x }^{ 2 } }{ 2 } \quad -(B-3)x\quad -(B+1)\\ h(x)=\quad { 4x }^{ 2 }\quad +36x\quad +32\\ 0={ \quad 4x }^{ 2 }\quad +36x\quad +32\\ 0=\quad (4x+4)(x+8)\\ x=\{ -1,-8\} \\ Since\quad the\quad zeroes\quad of\quad j(x)\quad are\quad the\quad double\quad of\quad the\quad zeroes\quad of\quad h(x),\quad \\ then\quad -2\quad and\quad -16\quad are\quad the\quad zeroes\quad of\quad j(x).\\ Let:\\ { r }_{ 1 }\quad =\quad 2\quad and\quad { r }_{ 2 }\quad =\quad -16\\ j(x)\quad =\quad (x-{ r }_{ 1 })(x-{ r }_{ 2 })\\ j(x)\quad =\quad (x+2)(x+16)\\ j(x)\quad =\quad { x }^{ 2 }\quad +18x\quad +32,\quad where\quad a=1,\quad b=18,\quad and\quad c=32.\\ For\quad a+b+c:\\ a+b+c=1+18+32\\ a+b+c=51\\ \\ Conjecture:\\ The\quad sum\quad of\quad a+b+c\quad of\quad the\quad standard\quad form\quad of\quad j(x)\quad is\quad 51.//

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