Maths-
General
Easy

Question

Find the value of ‘a’ if the three equations, (a + 1)3x + (a + 2)3 y = (a + 3)3, (a + 1) x + (a + 2)y = (a + 3) & x + y = 1 are consistent.

  1. –2    
  2. 2    
  3. –3    
  4. –6    

hintHint:

For the three equation to be consistent, the determinant must be 0.

The correct answer is: –2


    Step by step solution:
    Given three equations:
    left parenthesis a space plus space 1 right parenthesis cubed x space plus space left parenthesis a space plus space 2 right parenthesis cubedspace y space equals space left parenthesis a space plus space 3 right parenthesis cubed
    left parenthesis a space plus space 1 right parenthesis space x space plus space left parenthesis a space plus space 2 right parenthesisy space equals space left parenthesis a space plus space 3 right parenthesis
    x space plus space y space equals space 1
    For the three equation to be consistent, the determinant must be 0.
    Therefore, open vertical bar table row cell open parentheses a plus 1 close parentheses cubed end cell cell open parentheses a plus 2 close parentheses cubed end cell cell open parentheses a plus 3 close parentheses cubed end cell row cell open parentheses a plus 1 close parentheses end cell cell open parentheses a plus 2 close parentheses end cell cell open parentheses a plus 3 close parentheses end cell row 1 1 1 end table close vertical bar equals 0
    rightwards double arrow open parentheses a plus 1 close parentheses cubed left square bracket open parentheses a plus 2 close parenthesesnegative open parentheses a plus 3 close parentheses right square bracket minus open parentheses a plus 2 close parentheses cubedleft square bracket open parentheses a plus 1 close parentheses minus open parentheses a plus 3 close parentheses right square bracketplus open parentheses a plus 3 close parentheses cubedleft square bracket open parentheses a plus 1 close parentheses minus open parentheses a plus 2 close parentheses right square bracketequals 0
    rightwards double arrow open parentheses a plus 1 close parentheses cubed open parentheses negative 1 close parentheses minusopen parentheses a plus 2 close parentheses cubed open parentheses negative 2 close parenthesesplus open parentheses a plus 3 close parentheses cubed open parentheses negative 1 close parentheses equals 0
    rightwards double arrow negative open parentheses a cubed plus 3 a squared plus 3 a plus 1 close parenthesesplus 2 open parentheses a cubed plus 6 a squared plus 12 a plus 8 close parenthesesnegative 1 open parentheses a cubed plus 9 a squared plus 27 a plus 27 close parenthesesequals 0
    rightwards double arrow negative a cubed minus 3 a squared minus 3 a minus 1plus 2 a cubed plus 12 a squared plus 24 a plus 16negative a cubed minus 9 a squared minus 27 a minus 27equals 0
    rightwards double arrow negative 6 a minus 12 equals 0
    rightwards double arrow a equals negative 2
    Hence, option (a) is the correct option.

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