Q. 114.6( 7 Votes )

For what values of a and b, and x = — 2 are solutions of the equation ax2 + bx — 6 = 0.

Answer :

Put x = 3/4


ax2 + bx — 6 = 0





9a + 12b – 96 = 0 divide by 3


3a + 4b – 32 = 0


3a + 4b = 32 (1)


Put x = –2


ax2 + bx — 6 = 0


a(–2)2 + b(–2) – 6 = 0


4a – 2b – 6 = 0


4a – 2b = 6 (2)


Eliminate (1) and (2)


3a + 4b = 32


4a – 2b = 6 ×2



a = 4


Put a = 4 in equation (1).


3a + 4b = 32


3(4) + 4b = 32


12 + 4b = 32


4b = 32 – 12


4b = 20


b = 5


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