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ira [324]
3 years ago
14

Reese wants to organize a party and decides to save money for it.He calculates that he needs $420 in 9 weeks.He already has $60

Mathematics
1 answer:
amid [387]3 years ago
3 0
Start by creating an equation. You’ll need a variable to represent what is earned per week, for example x.

So,
420=60+9x
(Since he already has 60)
Subtract the 60 from 420 to begin isolating the variable
This gives you
360=9x
Divide both sides by 9 to completely isolate the variable
This gives you
40=x
So, he needs to save up $40 each week
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Find the function y1 of t which is the solution of 121y′′+110y′−24y=0 with initial conditions y1(0)=1,y′1(0)=0. y1= Note: y1 is
strojnjashka [21]

Answer:

Step-by-step explanation:

The original equation is 121y''+110y'-24y=0. We propose that the solution of this equations is of the form y = Ae^{rt}. Then, by replacing the derivatives we get the following

121r^2Ae^{rt}+110rAe^{rt}-24Ae^{rt}=0= Ae^{rt}(121r^2+110r-24)

Since we want a non trival solution, it must happen that A is different from zero. Also, the exponential function is always positive, then it must happen that

121r^2+110r-24=0

Recall that the roots of a polynomial of the form ax^2+bx+c are given by the formula

x = \frac{-b \pm \sqrt[]{b^2-4ac}}{2a}

In our case a = 121, b = 110 and c = -24. Using the formula we get the solutions

r_1 = -\frac{12}{11}

r_2 = \frac{2}{11}

So, in this case, the general solution is y = c_1 e^{\frac{-12t}{11}} + c_2 e^{\frac{2t}{11}}

a) In the first case, we are given that y(0) = 1 and y'(0) = 0. By differentiating the general solution and replacing t by 0 we get the equations

c_1 + c_2 = 1

c_1\frac{-12}{11} + c_2\frac{2}{11} = 0(or equivalently c_2 = 6c_1

By replacing the second equation in the first one, we get 7c_1 = 1 which implies that c_1 = \frac{1}{7}, c_2 = \frac{6}{7}.

So y_1 = \frac{1}{7}e^{\frac{-12t}{11}} + \frac{6}{7}e^{\frac{2t}{11}}

b) By using y(0) =0 and y'(0)=1 we get the equations

c_1+c_2 =0

c_1\frac{-12}{11} + c_2\frac{2}{11} = 1(or equivalently -12c_1+2c_2 = 11

By solving this system, the solution is c_1 = \frac{-11}{14}, c_2 = \frac{11}{14}

Then y_2 = \frac{-11}{14}e^{\frac{-12t}{11}} + \frac{11}{14} e^{\frac{2t}{11}}

c)

The Wronskian of the solutions is calculated as the determinant of the following matrix

\left| \begin{matrix}y_1 & y_2 \\ y_1' & y_2'\end{matrix}\right|= W(t) = y_1\cdot y_2'-y_1'y_2

By plugging the values of y_1 and

We can check this by using Abel's theorem. Given a second degree differential equation of the form y''+p(x)y'+q(x)y the wronskian is given by

e^{\int -p(x) dx}

In this case, by dividing the equation by 121 we get that p(x) = 10/11. So the wronskian is

e^{\int -\frac{10}{11} dx} = e^{\frac{-10x}{11}}

Note that this function is always positive, and thus, never zero. So y_1, y_2 is a fundamental set of solutions.

8 0
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nikitadnepr [17]

Answer:

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4 0
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Chrissy wants to spend at most $45 on dinner. If she bought an entree for $20 and she wants to buy mini appetizers for $3 each,
Sever21 [200]

Answer:

Step-by-step explanation:

Chrissy can buy 8 mini appetizers.......because

45 - 20 = 25

25 divide 3 = 8.3333333333333 so the most she can buy is 8..

:)

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Perimeters and Areas of Rectangles (PLEASE HELP)
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Answer:

i will only answer 11 and 4

Step-by-step explanation:

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6 0
2 years ago
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Find the coefficient of the x7y2term in the binomial expansion of (x+y)^9
statuscvo [17]

Answer:

36

Step-by-step explanation:

first, see the formula in the attached picture.

now, by applying that formula we get :

the coefficient of the x7y2 is :

9C7 = 36  (you can either use a calculator or just the algebraic formula)

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