How to turn a quadratic equation into an approximate number?

Question

x=-70plus or minuse sqaure root of 7300 over 4

A rectangular garden is to be surrounded by a walkway of constant width. The garden's dimensions are 30 ft by 40 ft. The total area, garden plus walkway, is to be 1800 ft2. What must be the width of the walkway to the nearest thousandth?

I solved it down to x= -70+/- sqaure root of 7300/4 and now I am lost

Answer 1

Put it in the quadratic formula and then use the calculator for a decimal approximation of the roots.
For example, x^2 + 5x + 3 = 0
Put this in the quadratic formula x = (-b +/- sqrt (b^2 - 4ac))/2a
with a = the coefficient on the first term (here, 1 is understood)
b = the coeffieint on the second term (here, 5)
c = the coefficient on the third term (here, 3)
Note: you must have the quadratic in standard form, with the terms in descending order, to match up the coefficients properly.)
so plug the numbers in
x = (-5 +/- sqrt (5^2 - 4x1x3))/(2x1) =
(-5 +/- sqrt 13)/2
Now put this into your calculator. be careful with order of opertaions, if in doubt, use parenthesis.
(-5 +/- 3.60555...)/2 =
approx -4.30277... or -0.697224...

Answer 2

Break it into the two roots:

x = (70 + sqrt 7300)/4 and

x = (70 - sqrt 7300)/4

If you have a good calculator you can enter it in just as I wrote it there....don't forget the brackets!

Answer 3

divide the square root of 7300 by 4 then add and subtract the answer to -70

Answer 4

Break it into two parts: one you add and the other you subtract.
So, you have two numbers:
[-70 + sqrt(7300) ]/ 4 or
[-70 - sqrt(7300) ] / 4