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Re: Which of the following is NOT a root of the equation [#permalink]
3
Equation gets very complicated if we solve the equation by algebra.so,we should use backsolving method.
always while using backsolving start from the middle option.
lets put the value x = 3;
(9+3-20)^2 - 2(9+3-20) - 63 =17
64 + 16 - 63
17
hence 3 is valid.

lets check x = 4;
(16+4-20)^2 - 2(16+4-20 ) - 63=17
0-63+17
here LHS is not equal to RHS

hence Answer is 4 option D.
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Re: Which of the following is NOT a root of the equation [#permalink]
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Strategy plug all answer choices in equation to get
L. H. S not equal to R. H. S
Which is only option: D.

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Re: Which of the following is NOT a root of the equation [#permalink]
2
You can say let y= x2+x-20
The equation then becomes
y2-2y-63=17
Y=-8
Y=10
Then substitute for values of Y in above equation.
X2+X-20+8=0
X=3
X=-4
Second part
X2+X-20-10=0
X=-6
X=5
Answer is D.
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Re: Which of the following is NOT a root of the equation [#permalink]
1
Let A = x2 + x - 20. The given complex algebraic equation reduces to: A^2 - 2A = 80 => A^2 - 2A + 1 = 81 => (A-1)^2 = 81 => A-1 = +/- 9 => A = 10 or A = -8.
After this just Plug in the options into A and only for x=4, A will be = 0 and others will either be = 10 or -8.
Hence, ans is D.
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