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 x-axis.

in general V = pi∫ y^2 dx

so you want

V = pi∫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 = pi∫(e4x+x3)^2 dx from 0 to .7

= pi∫(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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