- Write the matrix and use the given relation
Given
A=[1λ510],A−1=αA+βI
and
α+β=−2.
We use the identity
AA−1=I.
So,
A(αA+βI)=I⟹αA2+βA=I.
- Compute A2
A2=[1λ510][1λ510]=[1+5λλ+10λ5+505λ+100]=[1+5λ11λ555λ+100].
Hence,
αA2+βA=[α(1+5λ)+β11αλ+βλ55α+5βα(5λ+100)+10β].
Since this equals I=[1001], compare entries.
- Use off-diagonal entries
From the (1,2) entry:
55α+5β=0⟹11α+β=0.
Given also
α+β=−2.
Subtracting,
(11α+β)−(α+β)=0−(−2)
10α=2⟹α=51.
Then
β=−2−51=−511.
- Find λ
From the (2,1) entry:
11αλ+βλ=0⟹λ(11α+β)=0.
But already 11α+β=0, so this gives no new information.
Now use the (1,1) entry:
α(1+5λ)+β=1.
Substitute α=51, β=−511:
51(1+5λ)−511=1.
51+5λ−11=1⟹55λ−10=1
λ−2=1⟹λ=3.
- Compute the required expression
4α2+β2+λ2=4(51)2+(−511)2+32
=4⋅251+25121+9=254+121+9=25125+9=5+9=14.
- Final answer
14
So the correct option is D.