SOLUTION: If dy/dx is 6x^2+4x-5, and y=10 when x=2, find the value of y when x=3. please with full working

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Question 1152830: If dy/dx is 6x^2+4x-5, and y=10 when x=2, find the value of y when x=3. please with full working
Found 2 solutions by MathLover1, ikleyn:
Answer by MathLover1(20849)   (Show Source): You can put this solution on YOUR website!

If , then is


and when ,
let'c double check that:




=> is not = when ,must be:


find the value of when .





Answer by ikleyn(52776)   (Show Source): You can put this solution on YOUR website!
.

            It is very standard Calculus problem, typical for beginner Calculus students,
            and the solution by @MathLover1 is   A B S O L U T E L Y   W R O N G.

            Below find the correct solution,  instead.


Consider ANTIderivative, which is the general solution to the given differential equation

    y = 2x^3 + 2x^2 - 5x + C,    (1)

where C is an arbitrary constant.


We define the value of this constant from the given condition y= 10 at x= 2.


Substitute x= 2 into (1) to get

    10 = 2^2^3 + 2*2^2 - 5x + c,

    10 = 2*8 + 2*4 - 5*2 + C = 16 + 8 - 10 + C = C + 14,

which implies

    C = 10 - 14 = -4.


So, the specific solution to the given differential equation under the given condition at the point x= 2 is

    y = 2x^3 + 2x^2 - 5x - 4.    (2)


Now the value of y at x= 3 is

    y = 2*3^3 + 2*3^2 - 5*3 - 4 = 53.      ANSWER

Solved,  answered,  explained  (in all details)  and completed.


/\/\/\/\/\/\/\/\/

Having this text before your eyes,  printed or in the screen of your computer,
you may boldly go to a  Calculus class and to give a  PRESENTATION  (a lecture)
to students,  using my post as a  mantra,  even if you do not understand the subject,  at all.

You may use this post for many other similar problems,  with the equal success.


(It is partly a joke,  of course,  but partly is  TRUTH,  in great part . . . )



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