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Advanced Math / Nonlinear equations in one variable and systems of equations in two variables Difficulty: Hard

x 2 + y + 7 = 7

20x+100-y=0

The solution to the given system of equations is x,y. What is the value of x ?

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Explanation

The correct answer is -10 . Adding y to both sides of the second equation in the given system yields 20 x + 100 = y . Substituting 20 x + 100 for y in the first equation in the given system yields x2+20x+100+7=7. Subtracting 7 from both sides of this equation yields x 2 + 20 x + 100 = 0 . Factoring the left-hand side of this equation yields x+10x+10=0, or x+102=0. Taking the square root of both sides of this equation yields x + 10 = 0 . Subtracting 10 from both sides of this equation yields x = -10 . Therefore, the value of x is -10 .