math help! 987 = x^2 + 7x?

Question

987 = x^2 + 7x
how do you solve for x?

Answer 1

Why on Earth would one WANT a solution to such an awful equation, in the first place ?!

In any case, express it as a standard quadratic equation:

x^2 + 7 x - 987 = 0.

Then the two solutions are:

[- 7 +/- sqrt(49 + 4*987)] / 2 = [- 7 +/- sqrt(3997)] / 2 =
[- 7 +/- 63.2218] / 2.

Separating out the two solutions, they are:

x = 28.1109... and x = - 35.1109... .

CHECK (It's always worth doing a check.) One way is to substitute back in the original equation. The other is to check two things that must be true about the two solutions jointly:

1. They should add to - 7 (i.e.minus the coefficient of x). They do.

2. Their product should be - 987 (the "constant" term). Well,

- 35.1109... (28.1109...) = - 986.999...

--- as close as the number of significant figures will allow. So that confirms they're correct.

Live long and prosper.

Answer 2

Subtract 987 from both sides and you have a quadratic equation:
x^2 + 7x - 987 = 0
Use the quadratic formula if you do not immediately see the factors:
x = {-7 +- sqr[7^2 - 4(1)(-987)]}/2(1)
= {-7 +- sqr[3997]}/2 = {-7 +- sqr[(7)571]}/2
and here are your two answers

Answer 3

You would first subtract the 987 from both sides, creating a quadratic equation.

Now you use the quadratic formula to solve for x.

Answer 4

Usually you can just factor out with but that one you should just set it up as:

x^2 + 7x +987=0

Then use the quadratic formula. You can find the quadratic formula and how to use it here:

http://en.wikipedia.org/wiki/Quadratic_formula