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If there are two values of a which makes determinant, `Delta=|(1,-2,5),(2,a,-1),(0,4,2a)|=86` then the sum of these number isA. `4`B. `5`C. `-4`D. `9` |
Answer» Correct Answer - C We have `Delta=|(1,-2,5),(2,a,-1),(0,4,2a)|=86` `implies 1(2a^(2)+4)-2(-4a-20)+0=86` [expanding along first column] `implies 2a^(2)+4+8a+40=86` `implies 2a^(2)+8a+44-86=0` `implies a^(2)+4a-21=0` `implies a^(2)+7a-3a-21=0` `= (a+7)(a-3)=0` `a=-7` and `3` `:.` Required sum `=-7+3=-4` |
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