Maths-
General
Easy

Question

If A2 = 8A + kI where A = open square brackets table row 1 0 row cell negative 1 end cell 7 end table close square brackets then k is :

  1. 7    
  2. –7    
  3. 1    
  4. –1    

The correct answer is: –7


    open square brackets table attributes columnalign center center columnspacing 1em end attributes row cell 1 comma end cell 0 row cell negative 1 comma end cell 7 end table close square brackets open square brackets table attributes columnalign center center columnspacing 1em end attributes row cell 1 comma end cell 0 row cell negative 1 comma end cell 7 end table close square brackets = 8open square brackets table row cell 1 comma end cell 0 row cell negative 1 comma end cell 7 end table close square brackets + kopen square brackets table row 1 0 row 0 1 end table close square brackets
    or open square brackets table row cell 1 plus 0 end cell cell 0 plus 0 end cell row cell negative 1 minus 7 end cell cell 0 plus 49 end cell end table close square brackets = open square brackets table row 8 0 row cell negative 8 end cell 56 end table close square brackets +open square brackets table row k 0 row 0 k end table close square brackets
    or open square brackets table row 1 0 row cell negative 8 end cell 49 end table close square brackets = open square brackets table row cell k plus 8 end cell 0 row cell negative 8 end cell cell k plus 56 end cell end table close square brackets
    rightwards double arrow1 = k + 8
    49 = k + 56
    rightwards double arrowk = – 7

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