I'll start by mentioning that X^2+20X-8000 is not an equation.soumya_165 wrote:Hi All
Can anyone please help me out by solving the following equation using the formula
X^2+20X-8000
Formula: -b+-((b^2 - 4ac)^1/2)/2a
Hello Brent,Brent@GMATPrepNow wrote:I'll start by mentioning that X^2+20X-8000 is not an equation.soumya_165 wrote:Hi All
Can anyone please help me out by solving the following equation using the formula
X^2+20X-8000
Formula: -b+-((b^2 - 4ac)^1/2)/2a
I think you mean x^2 + 20x - 8000 = 0
I've never seen an official GMAT question that requires us to use of the Quadratic formula to solve an equation (even though the formula appears in the math review section of the Official Guide), but here goes . . .
The quadratic equation says:
If ax^2 + bx + c = 0, then x = [-b + sqrt(b^2 - 4ac)]/2a and x = [-b - sqrt(b^2 - 4ac)]/2a
In the given equation, a = 1, b = 20 and c = -8000
So, the two solutions are:
1) x = [-20 + sqrt(20^2 - (4)(1)(-8000)]/[2(1)]
= [-20 + 180]/2
= 160/2
= 80
2) x = [-20 - sqrt(20^2 - (4)(1)(-8000)]/[2(1)]
= [-20 - 180]/2
= (-200)/2
= -100
So, the solutions are x = 80 and x = -100
Cheers,
Brent
The equation posted on that link is tougher than most equations, but we can still solve it by factoring.lazarogb wrote:Hello Brent,Brent@GMATPrepNow wrote:I'll start by mentioning that X^2+20X-8000 is not an equation.soumya_165 wrote:Hi All
Can anyone please help me out by solving the following equation using the formula
X^2+20X-8000
Formula: -b+-((b^2 - 4ac)^1/2)/2a
I think you mean x^2 + 20x - 8000 = 0
I've never seen an official GMAT question that requires us to use of the Quadratic formula to solve an equation (even though the formula appears in the math review section of the Official Guide), but here goes . . .
The quadratic equation says:
If ax^2 + bx + c = 0, then x = [-b + sqrt(b^2 - 4ac)]/2a and x = [-b - sqrt(b^2 - 4ac)]/2a
In the given equation, a = 1, b = 20 and c = -8000
So, the two solutions are:
1) x = [-20 + sqrt(20^2 - (4)(1)(-8000)]/[2(1)]
= [-20 + 180]/2
= 160/2
= 80
2) x = [-20 - sqrt(20^2 - (4)(1)(-8000)]/[2(1)]
= [-20 - 180]/2
= (-200)/2
= -100
So, the solutions are x = 80 and x = -100
Cheers,
Brent
you might wanna check out a problem I just ran into with the gmat prep software extension package.
I think the gmat people expect us to know and be able to use the quadratic formula.
I posted it here:
https://www.beatthegmat.com/quadratic-fo ... tml#539832
thanks!
