Posted by sonia on Thursday, October 29, 2009 at 6:42pm.
Find the volume of the solid formed by rotating the region enclosed by
y=e^4x+3 y=0 x=0 x=0.7
this is my work
V = ∫ e^4x dx {between x=0 and x=0.7}
= 1/4 e^4x {between x=0 and x=0.7}
= 1/4 (e^2.8  e^0)
= 1/4 (e^2.8  1)
however i am etting the wrong answer pls help!!!

math  Reiny, Thursday, October 29, 2009 at 6:56pm
What you have found is the area of the region.
But you wanted the volume.
We also have to assume you are rotating about the xaxis.
in general V = piâˆ« y^2 dx
so you want
V = piâˆ«e^8x dx from 0 to .7
= (1/8)pi[e^8x] from 0 to .7
= (1.8)(pi(e^5.6  e^0)
= 105.8
You better check my arithmetic.

math  sonia, Thursday, October 29, 2009 at 7:01pm
Hi i checked the arithmitic and got 154.3699603 but this does not seem to be the right answer either what should I do??

math  Reiny, Thursday, October 29, 2009 at 7:08pm
Arggghhh!! I forgot the + 3 in the equation
try this
V = piâˆ«(e4x+x3)^2 dx from 0 to .7
= piâˆ«(e^8x + 6e^4x + 9)dx
= pi[(e^8x)/8 + (3/2)e^4x + 9x) from 0 to .7
= .... I will leave the arithmetic up to you, let me if it worked out this time.
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