1.

If `A = [(5a,-b),(3,2)]`and `A adj A=AA^T`, then `5a+b`is equal to:A. 5B. 4C. 13D. `-1`

Answer» Correct Answer - A
A adj `A=A A^(T)`
`implies |A|I=A A^(T)`
`implies (10a+3b) [(1,0),(0,1)]=[(5a,-b),(3,2)][(5a,3),(-b,2)]`
`implies 25a^(2)+b^(2)=10a+3b, 15a-2b=0, 10a+3b=13`
`implies 10a+(3.15a)/2=13`
`implies 65a=2xx13`
`implies a=2/5`
`implies 5a=2`
`implies 2b=6`
`implies b=3`
`:. 5a+b=5`


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