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Rudik [331]
2 years ago
14

Find constants a and b such that the function y = a sin(x) + b cos(x) satisfies the differential equation y'' + y' − 5y = sin(x)

.
Mathematics
1 answer:
vichka [17]2 years ago
8 0

Answers:

a = -6/37

b = -1/37

============================================================

Explanation:

Let's start things off by computing the derivatives we'll need

y = a\sin(x) + b\cos(x)\\\\y' = a\cos(x) - b\sin(x)\\\\y'' = -a\sin(x) - b\cos(x)\\\\

Apply substitution to get

y'' + y' - 5y = \sin(x)\\\\\left(-a\sin(x) - b\cos(x)\right) + \left(a\cos(x) - b\sin(x)\right) - 5\left(a\sin(x) + b\cos(x)\right) = \sin(x)\\\\-a\sin(x) - b\cos(x) + a\cos(x) - b\sin(x) - 5a\sin(x) - 5b\cos(x) = \sin(x)\\\\\left(-a\sin(x) - b\sin(x) - 5a\sin(x)\right)  + \left(- b\cos(x) + a\cos(x) - 5b\cos(x)\right) = \sin(x)\\\\\left(-a - b - 5a\right)\sin(x)  + \left(- b + a - 5b\right)\cos(x) = \sin(x)\\\\\left(-6a - b\right)\sin(x)  + \left(a - 6b\right)\cos(x) = \sin(x)\\\\

I've factored things in such a way that we have something in the form Msin(x) + Ncos(x), where M and N are coefficients based on the constants a,b.

The right hand side is simply sin(x). So we want that cos(x) term to go away. To do so, we need the coefficient (a-6b) in front of that cosine to be zero

a-6b = 0

a = 6b

At the same time, we want the (-6a-b)sin(x) term to have its coefficient be 1. That way we simplify the left hand side to sin(x)

-6a  -b = 1

-6(6b) - b = 1 .... plug in a = 6b

-36b - b = 1

-37b = 1

b = -1/37

Use this to find 'a'

a = 6b

a = 6(-1/37)

a = -6/37

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The cost and revenue functions for producing and selling x units of a product are given. Cost and revenue are expressed in dolla
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Answer:

(A) the number of units produced and sold at break-even point is the value of X and that is 1.126 units.

(B) the dollar amount coming in and going out at this point/level is the price of X and that is 0.37 dollars

(C) the profit function for X units produced and sold is: π(x) = R(x) - C(x)

where pie (the symbol "π") represents PROFIT.

Step-by-step explanation:

(A) C(x) = 75x + 84 ...(equation 1)

660R(x) = 245x

R(x) = 245x ÷ 660 = 0.3712x

So R(x) = 0.3712x ...(equation 2)

To find X, equate the cost function to the revenue function

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Since quantity cannot be negative in real life situation, we use the modulus of X in place of the above value.

|X| = 1.126 hence X = 1.126 now

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Break-even point is the point where cost = revenue

This is also the point where profit is zero because profit = revenue - cost

(B) Revenue = Price × Quantity

R = P×Q

Our revenue here is 0.3712x

Which is equal to 0.418 dollars

So P = R÷Q

Price = 0.418÷1.126 = 0.37 dollars

(C) This is the profit function from producing and selling X units of the product: π(x) = R(x) - C(x)

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