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Let's gather and simplify the inequality:

k^4 + 2k < 2k^3 + k^2

k(k-2)(k+1)(k-1) < 0 hence the inequalit is satisfied for -1 < k<0 V 1<k<2

if we have the constraint that k must be integer, then no value of k solves the inequality!

IMO A!
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I'd rearrange the inequality to make things easier for myself.

k^4 + 2k < 2k^3 + k^2

=> k^4 - 2k^3 - k^2 + 2k < 0.

What this means is, we take an integer value, and raise it to the power of 4, then deduct the double of the integer cubed, then deduct the integer squared, and add twice the integer, and expect the answer to still be below 0.

Now, the larger the integer gets, the higher the jump from k^3 to k^4. For instance, 2^3 is 8, and 2^4 is 16, double of it. But 8^3 is 512, and 8^4 is 4096, eight times the value.

You can see that:

8^4 - 2*8^3 - 8^2 + 2*8 = 4096 - 1024 - 64 + 16 = 3,024.

So, we're playing with really small values.

Let's take 1, the obvious starting point.

This will just be:

1 - 2 - 1 + 2 < 0, which is less than zero, so we do have that one value.

Taking 0 will just make it 0 = 0, so that doesn't work.


2 then:


16 - 16 - 4 + 4 = 0; 2 also won't work.

There's no point of going further into 3 upwards, given the reasoning above.

We can check out negative integers:

-1 will be:

-1^4 - (2*-1^3) - (-1^2) + 2(-1)

=> 1 - (-2) - 1 - 2

=> 1 + 2 - 1 - 2 = 0.

- 1 won't work.

It won't be any different for minus 2 onwards either, so no point checking those integers.

We can really only use one answer - 1 - here, hence the option that's correct is B: 1.

Bunuel
For how many integer values of k is k^4 + 2k < 2k^3 + k^2?

A. 0
B. 1
C. 2
D. 4
E. More than 4

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Bunuel
For how many integer values of k is k^4 + 2k < 2k^3 + k^2?

A. 0
B. 1
C. 2
D. 4
E. More than 4

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Given Inequality: k^4 + 2k < 2k^3 + k^2

k^4 - k^2 < 2k^3 - 2k

k^2 (k^2 -1 ) < 2k (k^2 - 1)
k(k-2)(k-1)(k+1) < 0

k cannot be -1,0,1,2 (product will be 0)

if k >= -2 , product is positive as all numbers will be -ve
if k <=3, product is positive as all numbers will be +ve

No integer solution
Correct Answer: A
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k^4 + 2k < 2k^3 + k^2
<=> k^2(k^2-1) - 2k(k^2-1) < 0
<=> (k^2-2k)(k^2-1) < 0
<=> k(k-2)(k-1)(k+1) < 0 (i)

So we have 4 points -1, 0, 1 , 2 to consider.

k < -1 => k < 0, k-2 < 0, k-1 < 0, k+1 < 0 => k(k-2)(k-1)(k+1) > 0
-1 <= k <= 0 => k(k-2)(k-1)(k+1) < 0
0 < k < 1 => k(k-2)(k-1)(k+1) > 0
1 <= k <= 2 => k(k-2)(k-1)(k+1) < 0
k > 2 => k(k-2)(k-1)(k+1) > 0

So for -1 <= k <= 0 and 1 <= k <= 2, these satisfy (i), however, k is integer, thus there is no value for k

Answer: A

Bunuel
For how many integer values of k is k^4 + 2k < 2k^3 + k^2?

A. 0
B. 1
C. 2
D. 4
E. More than 4

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k^4 + 2k < 2k^3 + k^2 <0
k^4 + 2k- 2k^3 -k^2 <0
k(k^3 - 2k^2 +2 -k) <0
k(k^2(k-2)-1(k-2))
k(k-2)(k^2-1) <0
k(k-2)(k-1)(k+1)<0
k = 0, 1, 2, -1
there are no integers in this range that satisfies the given equation
Option A, 0
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k^4 + 2k < 2k^3 + k^2
k^4 -2k^3 -k^2 +2k <0
k(k^3 -2k^2 -k +2) <0
k[(k^2)(k-2)-1(k-2)] <0
k(k-2)(k-1)(k+1) <0
We get the results to be 0 when k is -1,0,1,2. We want the expression to be negative. There are no values of k that satisfy the above equation. Thus, no integers satisfy the above inequality.

A. 0
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k^4 + 2k < 2k^3 + k^2
k^4 - 2k^3 - k^2 + 2k < 0
k(k^3 - 2k^2 - k + 2) < 0
k(k^2(k - 2) - (k - 2)) < 0
k(k - 2)(k^2 - 1) < 0
k(k - 2)(k - 1)(k + 1) < 0
(k - 2)(k - 1)k(k + 1) < 0

Product of four consecutive integers.
If all the integers are positive -> product is positive
If all the integers are negative -> product is positive

If there are positive and negative integers, then, for sure, one of the integers is 0, so the product is 0.

It's never negative. 0 integer values of k satisfy the inequality.

IMO A
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Solving the inequality,
k^4 - 2k^3 -k^2 + 2k < 0
k^3(k-2) - k(k - 2) <0
(k^3 - k )(k-2)<0

(k)(k^2-1)(k-2) <0
(k)(k+1)(k-1)(k-2)<0

The critical points are at -1 0 1 2

For less than 0,
1<k<2
-1<k<0

Since k needs to be an integer value, there is no integer in these intervals. Hence answer is 0


Bunuel
For how many integer values of k is k^4 + 2k < 2k^3 + k^2?

A. 0
B. 1
C. 2
D. 4
E. More than 4

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Given Inequality

K^4 +2k<2k^3 +k^2

K^4-2k^3-k^2+2k <0

(K^4-2k^3) - (k^2-2k)
K^3(k-2) - k (k-2)
k-2(k^3-k)
k^3-k = k(k-1)(k+1)
(k-2)k(k-1)(k+1)<0

A product is negative if and only if it has an odd number of negative factors.

Factors will change sign at K= -1,0,1,2
For interval k<-1 , sign
k-2. -ve
k -ve
k-1 -ve
k+1 -ve

4 neg - product positive

Interval 2 : -1<k<0(k= - 0.5)

k-2 -
k -
k-1 -
k+1 +ve

3 negatives - produc negative
But there is no integer between -1 and 0

Interval 3 : 0<k<1 (example k =0.5)
2 -ve = product positive

Interval 4 : 1<k<2 (example k =1.5)
1 neg - product neg
But there is no integer between 1 and 2

Interval 5 : K>2(ex k =3)
O negatives= product positive

There is no integer k for which inequality is satisfied , There ans is 0
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If you open this equation:

K(K^3 + 2) < K (K + 2K^2)

so we know one this K cannot be zero and will cancel K from both side using two condition since it is inequality.

assume K > 0

then (K^3 + 2) < K +2K^2 ------ 1

and K < 0

then K^3 + 2 > K + 2K^2 -------2

so when you will open this then
1 will be (K+1) (K-1) (K-2) < 0
similarly 2

so we know K cant be -1 , 1 or 2
also K <= -2 and K >= 2 will also not solve the above equation

Hence zero solution

Hence (A)
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Equation we have to solve for k is,
k^4 + 2k < 2k^3 + k^2
=> k^4 -2k^3 -k^2 + 2k < 0
=> k(k-1)(k+1)(k-2) < 0

=> k = -1,0,1,2 at which equation is 0
We want integer values of k which satisfy the equation i.e integer values where the above equation gives negative value

=> Intervals (-1,0) and (1,2) satisfy this
But there is no integers between these values

=> No integer values of k satisfy the inequality

A. 0
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K^4-K^2<2k^3-2K

K^2(K^2-1)<2k(K^2-1)

K^2(K^2-1) - 2K(K^2-1)<0

k(k + 1)(k - 1)(k - 2)<0

Use wavy line method to plot K=0,1,-1 and 2

Intervals where K<0 are -1<k<0 and 1<k<2

No integers falls in between this range, hence, 0.

Option A

Bunuel
For how many integer values of k is k^4 + 2k < 2k^3 + k^2?

A. 0
B. 1
C. 2
D. 4
E. More than 4

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k^4 + 2k < 2k^3 + k^2

all terms in one side:
k^4 - 2k^3 - k^2 + 2k < 0
k^3(k - 2) - k(k - 2) < 0
(k^3 - k)(k - 2) < 0
k(k^2 - 1)(k - 2) < 0
k(k - 1)(k + 1)(k - 2) < 0
(k - 2)(k - 1)k(k + 1) < 0

If k=-1 (-3)*(-2)*(-1)*0 = 0
If k=0 (-2)*(-1)*0*1 = 0
If k=1 (-1)*0*1*2 = 0
If k=2 0*1*2*3 = 0

If k<-1 or k>2 then the expression is positive. No integer value of k makes the expression negative.

Answer A
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k^4 + 2k < 2k^3 + k^2
k^4 - 2k^3 - k^2 + 2k < 0
k^2(k^2 - 1) - 2k(k^2 - 1) < 0
(k^2 - 2k)(k^2 - 1) < 0
k(k-2)(k+1)(k-1) < 0

If k=-1,0,1 or 2 then k(k-2)(k+1)(k-1)=0

For any other value of k there are 4 integers with the same sign, so their product is positive.

The are 0 integer values of k.

The answer is A
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Solve the inequality => k^4+2k < 2k^3+k2
bring all terms to one side => k^4-2k^3-k^2+2k<0
Factoring => k(k-2)(k-1)(k+1) <0
Critical values => -1,0,1,2
So solutions : (-1,0)U(1,2)

=> There are no solutions present. => A => 0
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k^4+2k < 2k^3+k^2

All in one side:
k^4-2k^3-k^2+2k < 0

Factor k:
k*(k^3-2k^2-k+2) < 0

Factor (k-2):
k(k^2(k-2)-(k-2)) < 0
k(k-2)(k^2-1) < 0
k(k-2)(k+1)(k-1) < 0

The multiplication of 4 consecutive integers can only be zero or positive, never negative. 0 values of k.

The correct answer is A
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K is an integer and after solving we see that inequality will be true in below interval
(-1,0) U (1,2) with no integer value. So, answer is zero.
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