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If x 2 + x − 2 = 3 , then what are the possible values for x ?
All possible values for x can be written in the form ± d a ± b c , where a , b , c , and d are the same coprime positive integers for all the value of x , but the ± signs can alter between + and − . What is a + b + c + d + 2 ?
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x 2 + x − 2 x 2 + x 2 1 x 2 − 2 + x 2 1 ( x − x 1 ) 2 x − x 1 = 3 = 3 = 1 = 1 = ± 1 Add − 2 on both sides. Take square root on both sides.
⟹ ⎩ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎨ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎧ x 2 − x − 1 x 2 + x − 1 = 0 = 0 ⟹ ⎩ ⎪ ⎪ ⎪ ⎪ ⎪ ⎨ ⎪ ⎪ ⎪ ⎪ ⎪ ⎧ x = 2 1 + 5 = ( 2 1 + 5 ) 2 = 2 3 + 5 x = 2 1 − 5 = − ( 2 5 − 1 ) 2 = − 2 3 − 5 ⟹ ⎩ ⎪ ⎪ ⎪ ⎪ ⎪ ⎨ ⎪ ⎪ ⎪ ⎪ ⎪ ⎧ x = 2 − 1 + 5 = ( 2 5 − 1 ) 2 = 2 3 − 5 x = 2 − 1 − 5 = − ( 2 1 + 5 ) 2 = − 2 3 + 5
Therefore, a + b + c + d + 2 = 3 + 1 + 5 + 2 + 2 = 1 3 .
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x 2 + x − 2 = 3
x 2 + x 2 1 = 3 → x 2 = q
q + q 1 = 3
q − 3 + q 1 = 0
q 2 − 3 q + 1 = 0
q = 2 3 ± 5
x = ± 2 3 ± 5
a = 3
b = 1
c = 5
d = 2
3 + 1 + 5 + 2 + 2 = 1 3