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Algebra Level 3

The length, breadth and height of a cuboid are roots of the polynomial: x 3 23 x 2 + 167 x 385. x^3-23x^2+167x-385. If the area and volume of that cuboid are A A and V , V, respectively, what is the value of A + V + 1010 ? A+V+1010?


The answer is 1729.

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6 solutions

Sujoy Roy
Dec 7, 2014

Let length, breadth and height (or roots of the given polynomial) of the cuboid are l , b l, b and h h respectively.

Now, A = 2 ( l b + b h + h l ) = 2 167 = 334 A=2(lb+bh+hl)=2*167=334 and V = l b h = 385 V=lbh=385 .

So, A + V + 1010 = 334 + 385 + 1010 = 1729 A+V+1010=334+385+1010=\boxed{1729} .

The answer just happens to be the Hardy-Ramanujan number. Concidence?

tytan le nguyen - 6 years, 5 months ago

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I think not. :D

Prasun Biswas - 6 years, 5 months ago

The Hardy-Ramanujan Number!

Swapnil Das - 6 years ago
Kenneth Tay
Jan 15, 2015

I think that it might be clearer if you said "surface area" of the cuboid rather than just "area"?

I agree... because "area" may mean lateral surface area or the surface area.

Rhoy Omega - 6 years, 4 months ago

it may have been clearer but still, in most cases area generally means total surface area only (unless stated otherwise).

sakshi taparia - 6 years, 4 months ago
Paola Ramírez
Jan 15, 2015

By Vieta's formula

l b + b h + h l = 167 lb+bh+hl=167

A = 2 ( l b + b h + h l ) = 334 A= 2(lb+bh+hl)=334

V = l b h = 385 V=lbh=385

A + V + 1010 = 334 + 385 + 1010 = 1729 A+V+1010=334+385+1010=\boxed{1729}

Alsro the polynomial can be factored by Synthetic Division

Fidel Simanjuntak
Aug 26, 2016

Let length be l l , breadth be b b and height be h h . The equation is

a x ³ + b x ² + c x + d = x ³ 23 x ² + 167 x 385 = 0 ax³+bx²+cx+d=x³-23x²+167x-385= 0

a = 1 , b = 23 , c = 167 , d = 385 a=1, b=-23, c=167, d=-385

From the Vieta's Formula, we get

l b h = d a = 385 lbh= \frac{-d}{a} = 385

l b + b h + l h = c a = 167 lb+bh+lh= \frac{c}{a} = 167

2 ( l b + b h + l h ) = 2 × 167 = 334 2(lb+bh+lh) = 2 \times 167 = 334

Now,

A + V + 1010 = 334 + 385 + 1010 A+V+1010 = 334 + 385 + 1010

= 1729 = \boxed{1729}

Let ( x a ) ( x b ) ( x c ) = x 3 23 x 2 + 167 x 385 = 0 (x-a)(x-b)(x-c)= x^3-23x^2+167x-385=0

Expanding the first expression x 3 ( a + b + c ) x 2 + ( a b + a c + b c ) x a b c = 0 x^3-(a+b+c)x^2+(ab+ac+bc)x-abc=0

A = 2 ( a b + b c + a c ) = 334 A=2(ab+bc+ac)=334

V = a b c = 385 V=abc =385

Then 385 + 334 + 1010 = 1729 385+334+1010=1729

Eugene Chong
Feb 14, 2015

Isn't the value of A a negative number? Since the sum of two roots are negative. Could someone please clarify? Thanks

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