# Investigate for What Values of μ and λ the Equations X+Y+Z=6, X+2y+3z=10, X+2y+λZ=μ Has 1) No Solution 2) a Unique Solution 3) Infinite Number of Solutions. - Applied Mathematics 1

Sum

Investigate for what values of μ and λ the equations x+y+z=6, x+2y+3z=10, x+2y+λz=μ has
1) No solution
2) A unique solution
3) Infinite number of solutions.

#### Solution

we have [(1,1,1),(1,2,3),(1,2,lambda)] [(x),(y),(z)]=[(6),(10),(mu)]

by R_2-R_1,    R_3-R_2

[(1,1,1),(0,1,2),(0,0,lambda-3)] [(x),(y),(z)]=[(6),(4),(mu-10)]

i) The system has unique solution if the coefficient matrix is non-singular (or the rank A, r = the number of unknowns, n=3).
This requires λ-3 not equal to 0, Hence λ is not equal to 3.
Hence the system has unique solution.

ii) If λ=3 the coefficient matrix and the augmented matrix becomes

[(1,1,1),(0,1,2),(0,0,0)] and [(1,1,1,6),(0,1,2,4),(0,0,0,mu-10)]

The rank of A=2 the rank of [A,B] will be also 2 if μ=10.
Thus if λ=3 and μ=10 the system is consistent. But the rank of A (=2) is less than the number of unknowns (=3). Hence the equation will posses infinite solutions.

iii) If λ=3 and μ≠10, the rank of A=2, and the rank of [A,B]=3. They are not equal and the equations will be inconsistent and will not posses any solution.

Concept: consistency and solutions of homogeneous and non – homogeneous equations
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