Evaluate ∫ ∫ ∫ ( X + Y + Z ) D X D Y D Z Over the Tetrahedron Bounded by the Planes X = 0, Y = 0, Z = 0 and X + Y + Z = 1. - Applied Mathematics 2

Evaluate int int int (x+y+z) dxdydz  over the tetrahedron bounded by the planes x = 0, y = 0, z = 0 and x + y + z = 1.

Solution

I=int_(x=0)^1 int_(y=0)^(1-x) int_(z=0)^(1-x-y) (x+y+z)dzdydx

I= int_(x=0)^1 int_(y=0)^(1-x) [(x+y+z)^2/2]^(1-x-y) dydz

I=1/2 int_(x=0)^1 int_(y=0)^(1-x) [1-(x-y)^2]dydx

I=1/2 int_(x=0)^1 [y-(x+y)^2/2]^(1-x) dx

I=1/2int_(x=0)^1 [(1-x)-1/3+x^3/3]dx

I=1/2 [(2x)/3+x^2/2+x^4/12]_0^1

I= 1/2. 3/12=1/8

∴I=1/8

Concept: Linear Differential Equation with Constant Coefficient‐ Complementary Function
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