Find the value of x for which the below given expression has a solution
x 2 − x − 2 x 2 + x − 2 = x − 2 x + 2
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First, cross multiplying to get ( x − 2 ) ( x 2 + x − 2 ) = ( x + 2 ) ( x 2 − x − 2 ) Simplifying a bit to get 2 x 2 − 8 = 0 2 ( x − 2 ) ( x + 2 ) = 0 Then, we have x = 2 or x = − 2 as our solutions. Notice that if we substitute x = 2 to the equation, the RHS will become 0 4 which is undefined. Thus, the only solution to this equation is x = − 2 .
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Factor the quadratics on the left hand side:
x 2 − x − 2 x 2 + x − 2 = ( x − 2 ) ( x + 1 ) ( x + 2 ) ( x − 1 )
We substitute and see
( x − 2 ) ( x + 1 ) ( x + 2 ) ( x − 1 ) = x − 2 x + 2
This equation takes the form a b = a , where a = x − 2 x + 2 and x + 1 x − 1 = b .
This form of equation has solutions for b = 1 or a = 0 . (Verify by subtracting a , factoring and applying the zero product property.)
But if b = x + 1 x − 1 = 1 , x − 1 and x + 1 , which differ by 2, must be equal, b = 1 does not lead to any solution.
Otherwise we consider a = x − 2 x + 2 = 0 , which holds if the numerator, x + 2 = 0 , giving x = − 2 as the unique solution.