Solve the following quadratic equations.

Algebra Level 1

Do it in thirty seconds!


The answer is 1.

Shelly Ding by Shelly Ding , 20, China

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2 solutions

Caleb Townsend
Feb 26, 2015

x 2 − x − 20 = 0 x^2 - x - 20 = 0 ( x − 5 ) ( x + 4 ) = 0 (x-5)(x+4) = 0 x 1 = 5 , x 2 = − 4 x_1=5,\ x_2=-4 x 1 + x 2 = 1 x_1 + x_2 = \boxed{1}

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First of all, there's a typo in the last line of your solution. Secondly, it can also be done orally in just a second or so using Vieta's formulas.

X 1 + X 2 = − (coefficient of x ) coefficient of x 2 = − ( − 1 ) 1 = 1 X_1+X_2=\frac{-\textrm{(coefficient of }x)}{\textrm{coefficient of }x^2}=\frac{-(-1)}{1}=\boxed{1}

Prasun Biswas - 6 years, 3 months ago

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Haha, yeah, that's what I did!

A Former Brilliant Member - 6 years ago

Did it in 3 seconds :D

Abdur Rehman Zahid - 6 years, 3 months ago
Marc Ballon
Nov 1, 2015

a^{2}x+bx+c=0.
Sum of roots=-b/a

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