Q. 234.0( 1 Vote )

Mark the correct alternative in the following:

If f : R R and g : R R are defined by f(x) = 2x + 3 and g(x) = x2 + 7, then the values of x such that g(f (x)) = 8 are

A. 1, 2

B. -1, 2

C. -1, -2

D. 1, -2

Answer :

g(f(x))=8

(f(x))2+7=8


(2x+3)2=1


4x2+12x+9=1


4 x2+12x+8=0


x2+3x+2=0


(x+1)(x+2)=0


x+1=0 or x+2=0


x=-1 or x=-2


Option C is correct..

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