You have a mixture of dimes and

Prove or disprove (from i=0 to n) sum([2i]^4) <= (4n)^4. If true use induction, else give the smallest value of n that it doe

ddd [48]

Answer:

The statement is true for every n between 0 and 77 and it is false for $n\geq 78$

Step-by-step explanation:

First, observe that, for n=0 and n=1 the statement is true:

For n=0: $\sum^{n}_{i=0} (2i)^4=0 \leq 0=(4n)^4$

For n=1: $\sum^{n}_{i=0} (2i)^4=16 \leq 256=(4n)^4$

From this point we will assume that $n\geq 2$

As we can see, $\sum^{n}_{i=0} (2i)^4=\sum^{n}_{i=0} 16i^4=16\sum^{n}_{i=0} i^4$ and $(4n)^4=256n^4$ . Then,

$\sum^{n}_{i=0} (2i)^4 \leq(4n)^4 \iff \sum^{n}_{i=0} i^4 \leq 16n^4$

Now, we will use the formula for the sum of the first 4th powers:

$\sum^{n}_{i=0} i^4=\frac{n^5}{5} +\frac{n^4}{2} +\frac{n^3}{3}-\frac{n}{30}=\frac{6n^5+15n^4+10n^3-n}{30}$

Therefore:

$\sum^{n}_{i=0} i^4 \leq 16n^4 \iff \frac{6n^5+15n^4+10n^3-n}{30} \leq 16n^4 \\\\ \iff 6n^5+10n^3-n \leq 465n^4 \iff 465n^4-6n^5-10n^3+n\geq 0$

and, because $n \geq 0$ ,

$465n^4-6n^5-10n^3+n\geq 0 \iff n(465n^3-6n^4-10n^2+1)\geq 0 \\\iff 465n^3-6n^4-10n^2+1\geq 0 \iff 465n^3-6n^4-10n^2\geq -1\\\iff n^2(465n-6n^2-10)\geq -1$

Observe that, because $n \geq 2$ and is an integer,

$n^2(465n-6n^2-10)\geq -1 \iff 465n-6n^2-10 \geq 0 \iff n(465-6n) \geq 10\\\iff 465-6n \geq 0 \iff n \leq \frac{465}{6}=\frac{155}{2}=77.5$

In concusion, the statement is true if and only if n is a non negative integer such that $n\leq 77$

So, 78 is the smallest value of n that does not satisfy the inequality.

Note: If you compute $(4n)^4- \sum^{n}_{i=0} (2i)^4$ for 77 and 78 you will obtain:

$(4n)^4- \sum^{n}_{i=0} (2i)^4=53810064$

$(4n)^4- \sum^{n}_{i=0} (2i)^4=-61754992$

7 0

3 years ago

Consider the following figure.

Karolina [17]

Answer:

BD = 16

Step-by-step explanation:

By applying mean proportional theorem in the given right triangles,

$\frac{AD}{BD}=\frac{BD}{CD}$

AD × CD = BD²

8 × 32 = BD²

BD = √256

BD = 16

Therefore, measure of side BD = 16 units.

4 0

2 years ago

What is the next term of the geometric sequence?<br>375,75,15

Damm [24]

Answer:

Step-by-step explanation:

ΔΔπФ⇵β³Δ⊄⊇≡⊕⊕π⇆ω∩∨

3 0

3 years ago

Read 2 more answers

Triangle A is reflected in the x-axis to give B.

nikitadnepr [17]

Answer:

The answer is below

Step-by-step explanation:

Transformation is the movement of a point from its initial location to a new location. Types of transformation is rotation, reflection, translation and dilation.

If a point A(x, y) is reflected over the x axis, the new point is at A'(x, -y). If a point B(x, y) is reflected over the y axis, the new point is at A'(-x, y).

Triangle A has vertex at (-4, -2), (-4, -5) and (-2, -5). If triangle A is reflected in the x axis to give triangle B, the vertex of triangle B is (-4, 2), (-4, 5) and (-2, 5).

If triangle B is reflected in the y axis to give triangle C, the vertex of triangle C is at (4, 2), (4, 5) and (2, 5). Hence the transformation is:

(x, y) ⇒ (-x, -y)

8 0

3 years ago

Which inequality is true? Use the number line to help

Nuetrik [128]

There is no image posted

6 0

3 years ago

Read 2 more answers