The length, breadth and height of a cuboid are roots of the polynomial: x 3 − 2 3 x 2 + 1 6 7 x − 3 8 5 . If the area and volume of that cuboid are A and V , respectively, what is the value of A + V + 1 0 1 0 ?
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The answer just happens to be the Hardy-Ramanujan number. Concidence?
The Hardy-Ramanujan Number!
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.
it may have been clearer but still, in most cases area generally means total surface area only (unless stated otherwise).
By Vieta's formula
l b + b h + h l = 1 6 7
A = 2 ( l b + b h + h l ) = 3 3 4
V = l b h = 3 8 5
A + V + 1 0 1 0 = 3 3 4 + 3 8 5 + 1 0 1 0 = 1 7 2 9
Alsro the polynomial can be factored by Synthetic Division
Let length be l , breadth be b and height be h . The equation is
a x ³ + b x ² + c x + d = x ³ − 2 3 x ² + 1 6 7 x − 3 8 5 = 0
a = 1 , b = − 2 3 , c = 1 6 7 , d = − 3 8 5
From the Vieta's Formula, we get
l b h = a − d = 3 8 5
l b + b h + l h = a c = 1 6 7
2 ( l b + b h + l h ) = 2 × 1 6 7 = 3 3 4
Now,
A + V + 1 0 1 0 = 3 3 4 + 3 8 5 + 1 0 1 0
= 1 7 2 9
Let ( x − a ) ( x − b ) ( x − c ) = x 3 − 2 3 x 2 + 1 6 7 x − 3 8 5 = 0
Expanding the first expression x 3 − ( a + b + c ) x 2 + ( a b + a c + b c ) x − a b c = 0
A = 2 ( a b + b c + a c ) = 3 3 4
V = a b c = 3 8 5
Then 3 8 5 + 3 3 4 + 1 0 1 0 = 1 7 2 9
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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Let length, breadth and height (or roots of the given polynomial) of the cuboid are l , b and h respectively.
Now, A = 2 ( l b + b h + h l ) = 2 ∗ 1 6 7 = 3 3 4 and V = l b h = 3 8 5 .
So, A + V + 1 0 1 0 = 3 3 4 + 3 8 5 + 1 0 1 0 = 1 7 2 9 .