Solve:    from Mathematics Differential Equations

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 Multiple Choice QuestionsShort Answer Type

181.

Solve:
cos space left parenthesis straight x plus straight y right parenthesis space dy over dx space equals space 1.

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 Multiple Choice QuestionsLong Answer Type

182.

Solve:
dy over dx space equals space tan space left parenthesis straight x plus straight y right parenthesis


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183. Solve the following initial value problem:
(x + y + 1)2 dy = dx, y ( –1) = 0
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184.

Solve the following initial value problem
cos (x + y) dy = dx, y (0) = 0

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185. For the following differential equation, given below, find  particular solution satisfying the given condition:
open parentheses straight x cubed plus straight x squared plus straight x plus 1 close parentheses dy over dx space equals space 2 straight x squared plus straight x semicolon space space straight y space equals space 1 space space when space straight x space equals space 0
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186. For the following differential equation, given below, find  particular solution satisfying the given condition:
straight x open parentheses straight x squared minus 1 close parentheses space dy over dx space equals space 1 space semicolon space space straight y space equals space 0 space space when space straight x space equals space 2

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 Multiple Choice QuestionsShort Answer Type

187. For the following differential equation, given below, find  particular solution satisfying the given condition:
cos space open parentheses dy over dx close parentheses space space equals straight a space space space left parenthesis straight a space element of space straight R right parenthesis semicolon space space space straight y space equals space 1 space space when space straight x space equals space 0


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188. For the following differential equation, given below, find  particular solution satisfying the given condition:
dy over dx equals straight y space tanx space semicolon space space straight y space equals space 1 space space when space straight x space equals space 0


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 Multiple Choice QuestionsLong Answer Type

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189.

Solve:   straight x squared dy over dx space equals straight x squared plus 5 xy plus 4 straight y squared.


The given differential equation is
                    straight x squared dy over dx space equals space straight x squared plus 5 xy plus 4 straight y squared
or                 dy over dx space equals space fraction numerator straight x squared plus 5 xy plus 4 straight y squared over denominator straight x squared end fraction
Put y = v x so that  dy over dx equals straight v plus straight x dv over dx
therefore space space space space space from space left parenthesis 1 right parenthesis comma space space straight v plus straight x dv over dx space equals fraction numerator straight x squared plus 5 straight x. space straight v space straight x space plus space 4 space straight v squared space straight x squared over denominator straight x squared end fraction
or      straight v plus straight x dv over dx space equals space 1 plus 5 straight v plus 4 straight v squared
or      straight x dv over dx space equals space 4 space straight v squared plus 4 space straight v space plus space 1
Separating the variables, we get,
                        fraction numerator 1 over denominator 4 space straight v squared plus 4 space straight v space plus space 1 end fraction dv space equals space 1 over straight x dx
Integrating    integral fraction numerator 1 over denominator 4 straight v squared plus 4 straight v plus 1 end fraction straight d space straight v space equals space integral 1 over straight x dx
or   integral fraction numerator 1 over denominator left parenthesis 2 space straight v space plus space 1 right parenthesis squared end fraction dv space equals space integral 1 over straight x dx space space space space space or space space space space integral left parenthesis 2 straight v plus 1 right parenthesis to the power of negative 2 end exponent space dv space equals space integral 1 over straight x dx
therefore space space space space fraction numerator left parenthesis 2 space straight v space plus space 1 right parenthesis to the power of negative 1 end exponent over denominator left parenthesis 2 right parenthesis space left parenthesis negative 1 right parenthesis end fraction space equals space log space open vertical bar straight x close vertical bar space plus straight c space space space space space or space space space space minus fraction numerator 1 over denominator 2 space left parenthesis 2 space straight v space plus 1 right parenthesis end fraction log space open vertical bar straight x close vertical bar plus straight c

or   negative fraction numerator 1 over denominator 2 open parentheses 2 begin display style straight y over straight x end style plus 1 close parentheses end fraction space equals space log space open vertical bar straight x close vertical bar plus straight c space space space space space space space space or space space space space space space space space space minus fraction numerator straight x over denominator 2 space left parenthesis straight x plus 2 space straight y right parenthesis end fraction space equals space log space open vertical bar straight x close vertical bar plus straight c

or      fraction numerator straight x over denominator 2 space left parenthesis straight x plus 2 space straight y right parenthesis end fraction plus log space open vertical bar straight x close vertical bar plus straight c space equals space 0

is the required solution. 
                           
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190.

Solve the following differential equation:
straight x squared dy over dx space equals space 2 xy plus straight y squared

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