1.

In a `4xx4` matrix the sum of each row, column and both the main diagonals is `alpha`. Then the sum of the four corner elementsA. is also `alpha`B. may not be `alpha`C. is never equal to `alpha`D. none of these

Answer» Correct Answer - A
Let `A=[a_(ij)]` be a `4xx4` matrix. It is given that
`a_(i1)+a_(i2)+a_(i3)+a_(i4)=alpha" for" i=1,2,3,4`
`a_(1j)+a_(2j)+a_(3j)+a_(4j)=alpha" for "j=1,2,3,4`
`a_11+a_22+a_33+a_(44)=alpha`
`anda_14+a_23+a_32+a_41=alpha`
We have to find `a_11+a_14+a_41+a_44`.
Clearly,
`(a_11+a_12+a_13+a_14)+(a_14+a_42+a_43+a_44)`
`+(a_11+a_22+a_33+a_44)+(a_14+a_23+a_32+a_41)`
`-(a_12+a_22+a_32+a_42)-(a_13+a_23+a_33+a_43)`
`=2(a_11+a_14+a_41+a_44)`
`rArr4alpha-2alpha=2(a_11+a_14+a_41+a_44)`
`rArr a_11+a_14+a41+a_44=alpha`


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