Q. Find the volume of the given solid,bounded by the cylinder y2+z2=64 and the planes x=2y,x=0,z=0 in the first octant
Set Up Triple Integral: To find the volume of the solid, we need to set up a triple integral in the appropriate coordinates. Since we are dealing with a cylinder, cylindrical coordinates might be a natural choice. However, since the bounds involve x and y explicitly, and we are only in the first octant, it might be simpler to use Cartesian coordinates. We will integrate over x, then y, then z.
Bounds for z: First, we need to determine the bounds for z. Since we are in the first octant and bounded by the cylinder y2+z2=64, z will range from 0 to the positive square root of (64−y2).
Bounds for y: Next, we determine the bounds for y. The solid is bounded by the plane x=2y and x=0. Since x=0 is the y-axis and we are in the first octant, y will range from 0 to 2x.
Bounds for x: Finally, we determine the bounds for x. The solid is bounded by the plane x=2y, but since we are in the first octant and y is bounded by the cylinder, we need to find the intersection of x=2y with the cylinder y2+z2=64. Substituting x=2y into the cylinder equation gives us (x/2)2+z2=64, which simplifies to x2/4+z2=64. Solving for x when z=0 gives us x=2y0. Therefore, x will range from x=2y2 to x=2y3.
Set Up Volume Integral: Now we can set up the triple integral for the volume V:V=∫∫∫dV, where dV=dzdydx. The limits of integration will be from z=0 to z=64−y2, y=0 to y=2x, and x=0 to x=16.
Integrate with Respect to z: The triple integral becomes:V=∫x=0x=16(∫y=0y=2x(∫z=0z=64−y2dz)dy)dx.
Integrate with Respect to y: We first integrate with respect to z: ∫z=0z=64−y2dz=[z]064−y2=64−y2.
Trigonometric Substitution: Substituting this into our integral, we get: V=∫x=0x=16(∫y=0y=2x64−y2dy)dx.
Simplify Integral: Next, we integrate with respect to y. This is a bit more complex, as it involves an integral of a square root function. We can use a trigonometric substitution, y=8sin(θ), dy=8cos(θ)dθ, and the integral becomes: ∫y=0y=x/264−y2dy=∫θ=0θ=arcsin(x/16)64−64sin2(θ)⋅8cos(θ)dθ.
Double Angle Formula: Simplifying the integral, we get: ∫θ=0θ=arcsin(16x)864(1−sin2(θ))⋅cos(θ)dθ=∫θ=0θ=arcsin(16x)64cos2(θ)dθ.
Evaluate Integral Bounds: This integral can be solved using the double angle formula for cosine, cos2(θ)=21+cos(2θ). The integral becomes:∫θ=0θ=arcsin(16x)64⋅21+cos(2θ)dθ=32∫θ=0θ=arcsin(16x)(1+cos(2θ))dθ.
Substitute Back into Integral: Integrating with respect to θ gives us: 32[θ+(1/2)sin(2θ)] from θ=0 to θ=arcsin(x/16).
Correct Error and Re-evaluate: Evaluating the integral at the bounds, we get: 32[arcsin(16x)+(21)sin(2arcsin(16x))]−32[0+(21)sin(0)].
Correct Error and Re-evaluate: Evaluating the integral at the bounds, we get: 32[arcsin(16x)+(21)sin(2arcsin(16x))]−32[0+(21)sin(0)].Since sin(2arcsin(16x))=2sin(arcsin(16x))cos(arcsin(16x)) and sin(arcsin(16x))=16x, cos(arcsin(16x))=1−(16x)2, the expression simplifies to: 32[arcsin(16x)+(21)(2(16x)1−(16x)2)].
Correct Error and Re-evaluate: Evaluating the integral at the bounds, we get: 32[arcsin(16x)+(21)sin(2arcsin(16x))] - 32[0+(21)sin(0)].Since sin(2arcsin(16x))=2sin(arcsin(16x))cos(arcsin(16x)) and sin(arcsin(16x))=16x, cos(arcsin(16x))=1−(16x)2, the expression simplifies to: 32[arcsin(16x)+(21)(2(16x)1−(16x)2)].Now we substitute this expression back into the integral for x and integrate from x=0 to x=16: V=∫x=0x=1632[arcsin(16x)+(8x)1−(16x)2]dx.
Correct Error and Re-evaluate: Evaluating the integral at the bounds, we get: 32[arcsin(x/16)+(1/2)sin(2arcsin(x/16))]−32[0+(1/2)sin(0)]. Since sin(2arcsin(x/16))=2sin(arcsin(x/16))cos(arcsin(x/16)) and sin(arcsin(x/16))=x/16, cos(arcsin(x/16))=1−(x/16)2, the expression simplifies to: 32[arcsin(x/16)+(1/2)(2(x/16)1−(x/16)2)]. Now we substitute this expression back into the integral for x and integrate from x=0 to x=16: V=∫x=0x=1632[arcsin(x/16)+(x/8)1−(x/16)2]dx. This integral is quite complex and typically requires numerical methods or special functions to evaluate. However, we have made a mistake in our setup. The upper limit for y should not be sin(2arcsin(x/16))=2sin(arcsin(x/16))cos(arcsin(x/16))0, but rather the intersection of the plane sin(2arcsin(x/16))=2sin(arcsin(x/16))cos(arcsin(x/16))1 with the cylinder sin(2arcsin(x/16))=2sin(arcsin(x/16))cos(arcsin(x/16))2 when sin(2arcsin(x/16))=2sin(arcsin(x/16))cos(arcsin(x/16))3. This means y should range from sin(2arcsin(x/16))=2sin(arcsin(x/16))cos(arcsin(x/16))5 to sin(2arcsin(x/16))=2sin(arcsin(x/16))cos(arcsin(x/16))6, not sin(2arcsin(x/16))=2sin(arcsin(x/16))cos(arcsin(x/16))0. We need to correct this error and re-evaluate the integral.
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