simple quadratic

Algebra Level 1

( x 1 ) 2 + x 1 + ( x 2 ) + x 2 = 0 (x-1)^2 + |x-1|+|(x^2 )+x-2|=0
x x is real. Find x x .

Hint: square of real number is always positive.


The answer is 1.

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8 solutions

Dominick Hing
Oct 24, 2014

All of the quantities are within absolute value signs. Thus if any of those quantities within the absolute value signs are anything other than 0, then the equation will not be true because anything in absolute value signs are either 0 or positive. Therefore x - 1 must equal zero.

Thus we can set x 1 = 0 x - 1 = 0 , so x must be 1.

Note that if you set x 2 x 2 = 0 { x }^{ 2 }-x-2=0 equal to zero, the -2 that we get as a solution is extraneous.

X = 1 X = 1

Mj Bltz
Oct 25, 2014

Since the term ( x 1 ) 2 (x-1)^2 can be rewritten as the product of identical terms in absolute value signs, and x 2 + x 2 = x + 2 x 1 \left | x^2 +x -2 \right |= \left | x+2 \right |\left | x-1 \right | , then we can rewrite the equation to the following form.

( x 1 ) 2 + x 1 + x 2 + x 2 = ( x 1 ) 2 + x 1 + x + 2 x 1 (x-1)^2 + \left | x-1 \right | + \left | x^2 +x -2 \right | = \left ( \left | x-1 \right | \right )^2 + \left | x-1 \right | + \left | x+2 \right |\left | x-1 \right |

Factoring out x 1 \left | x-1 \right | , we can solve for x.

x 1 ( x 1 + 1 + x + 2 ) = 0 \left | x-1 \right |(\left | x-1 \right | + 1 + \left | x+2 \right |) = 0

Since the sum of the terms in parentheses can't be equal to 0, then it must be that x = 1 x = 1 .

Renah Bernat
Oct 30, 2014

Let a = (x-1)^2, b = | x - 1 |, c = | x^2 + x -2 |. All terms (a, b, c) are positive so their summation can only be zero if each is zero. x=1 yields zero for each of the terms a,b, and c.

every time it need not be that their summation is 0 only IF EACH IS ZERO. it can also be that one is negative and other possitive even then they will be summing up to 0 only

Priyansh Choudhary - 6 years, 7 months ago

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Did you notice the | | sign of the last two terms and the square of the first term. Hence all the three terms should be >= 0. Given that they are real and their summation =0, each of them must be zero

Govind Balaji - 6 years, 7 months ago

Since the RHS is 0 the sum of the terms on the LHS is 0 and therefore all three terms must be 0. And x = 1 is the only value that solves the equation.

Leonardo Sipayung
Mar 19, 2015

So easy ... Just substitue x = 1 x=1 into the equation : ( x 1 ) 2 + x 1 + ( x 2 ) + x 2 = 0 (x-1)^2+|x-1|+|(x^2)+x-2|=0 ( 1 1 ) 2 + 1 1 + 1 2 + 1 2 = 0 (1-1)^2+|1-1|+|1^2+1-2|=0

( 0 ) 2 + 0 + 1 1 = 0 (0)^2+|0|+|1-1|=0

0 = 0 0=0

So we get x = 1

Aadi Naik
Oct 31, 2014

Each and every part inside the modulus sign is >=0 so we can say that it will be equal to 0 if we have (x-1)²=0

Siddhartha Nayak
Oct 31, 2014

As all the terms are positive and summing up of the positive terms can not be zero, so we have to make all terms equal to zero.....So we can say x-1=0 =>x=1.

Since each quantities are positive each of them must be 0. The only number for each quantity which makes them 0 is 1. x-1=0 and x=1

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