Let A and B be two square matrices of same order satisfying \(A^2+5A+5I=0\) and \(B^2+3B+I=0\) respectively. Where I is the identity matrix. Then the inverse of the matrix C = BA+2B+2A+4I is
Step-by-step Solution:
Correct Answer: A ($AB+A+3B+3I$)
To find the inverse of the matrix C, we will first simplify the expression for C, then find the inverses of its factors using the given polynomial equations for A and B.
The matrix C is given by $C = BA + 2B + 2A + 4I$. We can factor this expression by grouping:
$C = (BA + 2B) + (2A + 4I)$
$C = B(A + 2I) + 2(A + 2I)$
Factoring out the common term $(A+2I)$, we get:
$C = (B+2I)(A+2I)$
Using the property for the inverse of a product of matrices, $(XY)^{-1} = Y^{-1}X^{-1}$, we can write the inverse of C as:
$C^{-1} = ((B+2I)(A+2I))^{-1} = (A+2I)^{-1}(B+2I)^{-1}$
Our next task is to find the inverses of $(A+2I)$ and $(B+2I)$.
Finding $(A+2I)^{-1}$:
We use the given equation for A: $A^2 + 5A + 5I = 0$. We manipulate this equation to find a matrix X such that $(A+2I)X = I$.
$A^2 + 5A + 5I = 0$
$A^2 + 5A + 6I = I$
$(A^2 + 2A) + (3A + 6I) = I$
$A(A+2I) + 3(A+2I) = I$
$(A+3I)(A+2I) = I$
From this, we can see that the inverse of $(A+2I)$ is $(A+3I)$.
Finding $(B+2I)^{-1}$:
We use the given equation for B: $B^2 + 3B + I = 0$. We follow a similar procedure.
$B^2 + 3B + I = 0$
$B^2 + 3B + 2I = I$
$(B^2 + 2B) + (B + 2I) = I$
$B(B+2I) + 1(B+2I) = I$
$(B+I)(B+2I) = I$
From this, we can see that the inverse of $(B+2I)$ is $(B+I)$.
Now we substitute the individual inverses back into our expression for $C^{-1}$:
$C^{-1} = (A+2I)^{-1}(B+2I)^{-1} = (A+3I)(B+I)$
Finally, we expand this product:
$C^{-1} = A(B+I) + 3I(B+I)$
$C^{-1} = AB + AI + 3IB + 3I^2$
$C^{-1} = AB + A + 3B + 3I$