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klio [65]
3 years ago
11

The value of y varies directly with x, and y=28 when x=7. Find y when x=4 by first finding k.

Mathematics
1 answer:
lesya692 [45]3 years ago
7 0
Direct proportionality is the type of proportionality where an increase in one quantity or variable causes a corresponding increase in another quantity. 
Therefore; y varies directly as x
Hence; y α x
             y =k x where k is a constant 
if y= 28 and x = 7 , then k = 28/4 =4
hence, y = 4 k
when x = 4, then y= 16

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igomit [66]

Answer:

x=-cos(t)+2sin(t)

Step-by-step explanation:

The problem is very simple, since they give us the solution from the start. However I will show you how they came to that solution:

A differential equation of the form:

a_n y^n +a_n_-_1y^{n-1}+...+a_1y'+a_oy=0

Will have a characteristic equation of the form:

a_n r^n +a_n_-_1r^{n-1}+...+a_1r+a_o=0

Where solutions r_1,r_2...,r_n are the roots from which the general solution can be found.

For real roots the solution is given by:

y(t)=c_1e^{r_1t} +c_2e^{r_2t}

For real repeated roots the solution is given by:

y(t)=c_1e^{rt} +c_2te^{rt}

For complex roots the solution is given by:

y(t)=c_1e^{\lambda t} cos(\mu t)+c_2e^{\lambda t} sin(\mu t)

Where:

r_1_,_2=\lambda \pm \mu i

Let's find the solution for x''+x=0 using the previous information:

The characteristic equation is:

r^{2} +1=0

So, the roots are given by:

r_1_,_2=0\pm \sqrt{-1} =\pm i

Therefore, the solution is:

x(t)=c_1cos(t)+c_2sin(t)

As you can see, is the same solution provided by the problem.

Moving on, let's find the derivative of x(t) in order to find the constants c_1 and c_2:

x'(t)=-c_1sin(t)+c_2cos(t)

Evaluating the initial conditions:

x(0)=-1\\\\-1=c_1cos(0)+c_2sin(0)\\\\-1=c_1

And

x'(0)=2\\\\2=-c_1sin(0)+c_2cos(0)\\\\2=c_2

Now we have found the value of the constants, the solution of the second-order IVP is:

x=-cos(t)+2sin(t)

3 0
3 years ago
Suppose that 10% of all steel shafts produced by a certain process are nonconforming but can be reworked (rather than having to
balandron [24]

Answer:

0.9905,0.9837,0.8066

Step-by-step explanation:

Given that 10%  of all steel shafts produced by a certain process are nonconforming but can be reworked (rather than having to be scrapped).

Each shaft is independent of the other and probability for non conforming is the same for each trial.

Hence X the among these that are nonconforming and can be reworked. is Bin with n =200 and p = 0.10

a) P(X\leq 30) = 0.9905

b) P(X

c) P(15\leq x\leq 25)\\= F(25)-F(14)\\= 0.8995-0.0929\\= 0.8066

6 0
3 years ago
-8x+3=8x+27 I need help plz I’m trash at math
belka [17]

Answer:

-1.5

Step-by-step explanation:

<u>See steps below:</u>

  • -8x+3=8x+27
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Please help it's fricking urgent
Gwar [14]

Answer:

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Step-by-step explanation:

Ben = x

Kaden = x - 10

x + 4

x - 10 + 4 = x -6

x - 6 = \frac{7}{9} x

9(x - 6) = 7x

9x - 54 = 7x

2x = 54

x = 27

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5 0
3 years ago
Read 2 more answers
. log 3x4<br> Expand each expression
valentina_108 [34]

Answer:

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Step-by-step explanation:

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