Quadratic Equation

Algebra Level 1

Find the positive root of the equation x 2 + x 20 = 0 x^{2}+x-20=0 .


The answer is 4.

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4 solutions

x 2 + x 20 = 0 x^2+x-20=0

By factoring, we have

( x + 5 ) ( x 4 ) = 0 (x+5)(x-4)=0

x = 5 x=-5

x = 4 x=4

So the positive root is x = 4 \boxed{x=4} .

Note: We can also use the quadratic formula.

I prefer this.

Completing square.

It is the easiest way for me to solve quadratic equation .

. . - 1 month ago

x^2 +x - 20

this equals,

x^2 + 5x - 4x - 20

or,

x(x + 5) - 4(x + 5)

i.e.

(x - 4)(x + 5)

So, either x = 4 or x = -5

Hence positive root equals 4 !!!!!!

. .
May 8, 2021

x 2 + x 20 = 0 x ^ { 2 } + x - 20 = 0

( x 4 ) ( x + 5 ) = 0 ( x - 4 ) ( x + 5 ) = 0

x 4 = 0 , or x + 5 = 0 x - 4 = 0 \text { , or } x + 5 = 0 \

x = 4 , or x = 5 x = 4 \text { , or } x = -5

But, we are looking for the positive root, so it is x = 4 \boxed { \color{#3D99F6} x = 4 }

One way to solve this is by factoring.

x 2 + x 20 = 0 x^2+x-20=0

( x + 5 ) ( x 4 ) = 0 x+5)(x-4)=0

x + 5 = 0 x+5=0

x = 5 x=-5

or

x 4 = 0 x-4=0

x = 4 x=4

Therefore, the positive root is x = 4 x=4 .

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