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Lê Quốc Trần Anh Coordinator
16/08/2017 at 09:18
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An ice cream cone is 5 inches tall with a radius of 1.5 inches. The outer surface area of the cone is covered with chocolate. How many square inches of cone are covered with chocolate? Express your answer as a decimal to the nearest tenth.

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    Phan Thanh Tinh Coordinator 16/08/2017 at 09:41

    Applying the Pythagoras' theorem, we deduce that the length of slant is : \(\sqrt{5^2+\left(1.5\right)^2}=\dfrac{\sqrt{109}}{2}\) (inches)

    The area which is covered with chocolate is :

     \(1,5\pi.\dfrac{\sqrt{109}}{2}=\dfrac{3\pi\sqrt{109}}{4}=24.5993926...\approx24.6\)(square inches)

    Lê Quốc Trần Anh selected this answer.

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Summer Clouds moderators
30/08/2017 at 08:37
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 In the squares of the 4 x 4 board numbers are written such that the numbers in adjacent squares differ by 1. Numbers 3 and 9 appear in the table. Number 3 is in the top left corner as shown. How many different numbers appear in the table?  
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    Lê Quốc Trần Anh Coordinator 30/08/2017 at 12:57

    Every time you move, you need to change by 1. To get from 3-9, you must step through 7 different numbers (from 3 to 9). If you deduce 3-2-1-... you won't make to 9.

    So there are 7 different numbers.

    Selected by MathYouLike

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Summer Clouds moderators
14/09/2017 at 08:47
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Stacey has some pennies, nickels and dimes divided between her left and right pockets. She has the same number of coins in each pocket, and the coins in her two pockets add to the same total value. Stacey does not have the same number of pennies in each pocket. What is the minimum total value that she could have in both pockets combined? 

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    manhmiio 14/09/2017 at 22:01

    l do not know english,notvery clear


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Ngô Tấn Đạt
15/10/2017 at 12:05
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Find \(n\in N\); \(n^4-n+2\) is square of a number

 

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    Phan Thanh Tinh Coordinator 15/10/2017 at 23:23

    Consider 4 cases :

    + n = 0 => n4 - n + 2 = 2 (unsatisfied)

    + n = 1 => n4 - n + 2 = 2 (unsatisfied)

    + n = 2 => n4 - n + 2 = 16 = 42 (satisfied)

    + n > 2 

    \(\circledast n^4-n+2< n^4\)

    \(\circledast\left(n^4-n+2\right)-\left(n^2-1\right)^2=n^4-n+2-n^4+2n^2-1\)

    \(=2n^2-n+1=2\left(n^2-\dfrac{1}{2}n+\dfrac{1}{2}\right)\)

    \(=2\left(n^2-2n.\dfrac{1}{4}+\dfrac{1}{16}+\dfrac{7}{16}\right)=2\left(n-\dfrac{1}{4}\right)^2+\dfrac{7}{8}>0\)

    \(\Rightarrow\left(n^2-1\right)^2< n^4-n+2\)

    Hence, n4 - n + 2 is between two consecutive perfect squares : (n2 - 1)2 and (n2)2, so n4 - n + 2 is not a perfect square

    So, n = 2

    Selected by MathYouLike
  • ...
    Ngô Tấn Đạt 15/10/2017 at 12:05

    Phan Thanh Tinh Dao Trong Luan


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Lê Quốc Trần Anh Coordinator
13/11/2017 at 17:52
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The price of a shirt was reduced by 20%. Including the 5% sales tax, Cyndi paid $15.54 for the shirt. What was the original price of the shirt before the discount was applied?

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    Phan Thanh Tinh Coordinator 15/11/2017 at 12:04

    Let a be the original price of the shirt. We have :

    \(\left(1+5\%\right).\left(1-20\%\right)a=15.54\Leftrightarrow105\%.80\%a=15.54\) \(\Leftrightarrow a=18.5\)

    So, the answer is $18.50


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Cloud moderators
30/11/2017 at 13:52
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What is the sum of the positive integer factors of 2017?

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    Lê Quốc Trần Anh Coordinator 30/11/2017 at 18:04

    Because 2017 is a prime number

    => \(F\left(2017\right)=1;2017\)

    So their sum is: \(1+2017=2018\)

    Selected by MathYouLike
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    Vũ Mạnh Hùng 03/12/2017 at 20:32

    F=(2017) 1and 2017

    the sum is 1+2017=2018


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Alone
07/04/2018 at 13:59
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Prove that \(\dfrac{n}{\sqrt{n-1}}\ge2\) with \(n>1\)


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Lê Quốc Trần Anh Coordinator
11/06/2018 at 02:14
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Find \(n\in N\) so that \(n^5-n+2\) is a square number

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    Dao Trong Luan Coordinator 11/06/2018 at 12:10

    \(n^5-n+2=n\left(n^4-1\right)+2=n\left(n^2+1\right)\left(n^2-1\right)+2\)

    \(=n\left(n-1\right)\left(n+1\right)\left(n^2+1\right)+2\)

    We see: \(\left(n-1\right)\cdot n\cdot\left(n+1\right)⋮3\) (is product of 3 consecutive natural numbers) 

    \(\Rightarrow n^5-n+2\equiv2\left(mod3\right)\)

    But no square numbers are in the form 3k + 2

    So \(n\notin\varnothing\)

    Lê Quốc Trần Anh selected this answer.

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Lê Quốc Trần Anh Coordinator
08/07/2018 at 06:19
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For how many positive integers n is it possible to have a triangle with side lengths 5, 12 and n?

Mathcounts

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    Tôn Thất Khắc Trịnh 25/07/2018 at 06:52

    Applying the triangular inequality:
    \(12-5< n< 12+5\)
    \(\Leftrightarrow7< n< 17\)
    So n varies from 8 to 16, therefore there are 9 possible integer values of n


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Face586
03/08/2018 at 14:29
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Blue, red, yellow, yellow
The solitary paradise lying alone.
What is the quiz?

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    Cristiano Ronaldo 03/08/2018 at 14:30

    Blue, red, yellow, yellow
    The solitary paradise lying alone.
    What is the quiz?

    Answer: It's a rainbow


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Trigonometric
sin cos tan cot sinh cosh tanh
Lim-log

Combined operations

 

α β γ δ θ σ ∂ ε ω φ ϕ π μ λ Ψ ξ η χ ζ ι κ ν ψ Ω ρ τ υ Γ Δ Λ Φ Π Σ Υ Ξ ϑ Θ ς ϰ
∞ ⊻ ⩞ ⋎ ⋏ ≀ ∪ ⊎ ⋓ ∩ ⋒ ⊔ ⊓ ⨿ ⊗ ⊙ ⊚ ⊛ ⊘ ⊝ ⊕ ⊖ ⊠ ◯ ⊥
⇔ ⇒ ⇐ → ← ↔ ↑ ↓
Operations
+ - ÷ × ≠ = ⊂ ⊃ ⊆ ⊇ ≈ ∈ ∉ ∃ ∄ ≤ ≥ ± ∓ ≠ ∅ ≃ ≅ ≡ ⋮ ⋮̸ ∀
(□) [□] {□} |□|

The type of system

m×n 1×2 1×3 1×4 1×5 1×6
2×1 2×2 2×3 2×4 2×5 2×6
3×1 3×2 3×3 3×4 3×5 3×6
4×1 4×2 4×3 4×4 4×5 4×6
5×1 5×2 5×3 5×4 5×5 5×6
6×1 6×2 6×3 6×4 6×5 6×6

Recipe:

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