What am I doing wrong? Integration of y=x^2 + 4 between y=13, y=4, help appreciated! (1 Viewer)

[blackops23]

Hi, here's the question:

Find the area bound by the curve y=x^2 + 4 and the lines y=4, and y=13

So here's what I did.

x=(y-40)^0.5







=F(13) - F(4)

=[(13-4)^1.5]/1.5 - [(4-4)^1.5]/1.5
=18 - 0
=18

Answer was 36, what did I do wrong, seems like a silly mistake but I can't spot it.

Help appreciated, thanks

 

[Bored Of Fail 3]

Re: What am I doing wrong? Integration of y=x^2 + 4 between y=13, y=4, help appreciat

fairly sure you need to multiply that integral by 2

 

[Bored Of Fail 3]

Re: What am I doing wrong? Integration of y=x^2 + 4 between y=13, y=4, help appreciat

draw the diagram, you are only finding the area of the right hand side of the parabola with the y axis , you need to multiply it by 2

 

[ohexploitable]

Re: What am I doing wrong? Integration of y=x^2 + 4 between y=13, y=4, help appreciat

When you took the square root you only accounted for the positive half of the parabola,

 

[ohexploitable]

Re: What am I doing wrong? Integration of y=x^2 + 4 between y=13, y=4, help appreciat

 

[blackops23]

Re: What am I doing wrong? Integration of y=x^2 + 4 between y=13, y=4, help appreciat

i see... thankyou

 

[Bored Of Fail 3]

Re: What am I doing wrong? Integration of y=x^2 + 4 between y=13, y=4, help appreciat

question for you, similar one:

Find the volume of the solid formed when the curve y=x^2 +4 is rotated about the y axis between y=4 and y=13

 

[blackops23]

Re: What am I doing wrong? Integration of y=x^2 + 4 between y=13, y=4, help appreciat

question for you, similar one:

Find the volume of the solid formed when the curve y=x^2 +4 is rotated about the y axis between y=4 and y=13

not up to volumes yet

 

[jamesfirst]

Re: What am I doing wrong? Integration of y=x^2 + 4 between y=13, y=4, help appreciat

hmm didn't know you had to multiply it by 2 lol

I learned a new thing!! haha

 

[blackops23]

Re: What am I doing wrong? Integration of y=x^2 + 4 between y=13, y=4, help appreciat

hmm didn't know you had to multiply it by 2 lol

I learned a new thing!! haha

shit lol graphmatica fucking failed me, sketched x=+(y-4)^0.5, it gives me the whole fucking parabola, when the graph should be on the 1st quadrant only =(, probably should not rely on graphing software for everything, graph is simple enough =P so that's why you have to double it.

 

[blackops23]

Re: What am I doing wrong? Integration of y=x^2 + 4 between y=13, y=4, help appreciat

question for you, similar one:

Find the volume of the solid formed when the curve y=x^2 +4 is rotated about the y axis between y=4 and y=13

81pi/2? prolly made a mistake sumwhere did it in my head, anyways volumes is a 2u topic so i should be fine...