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Hey
Please help me understand how to solve the problem below. This one question stopped me from getting a hundred on the test! Thanks
Problem:
Given the function f(x) = x^2 + 2x - 99, list the x-intercepts, if any, of the graph of f.
My attempt:
f(x) = x^2 + 2x - 99
y = x^2 + 2x - 99
0 = x^2 + 2x - 99
99 = x^2 + 2x
99 - 2x = x^2
sqrt(99 - 2x) = x
(99 - 2x) / x = x
99 - 2 = x
97 = x
x-intercept is (97, 0)
Sam
Good workQuote:
Originally Posted by ArcherSam
Your mistake is where I have bolded it - You have introduced a square root and then forgotten about it in the next step!Quote:
99 = x^2 + 2x
99 - 2x = x^2
sqrt(99 - 2x) = x
(99 - 2x) / x = x
99 - 2 = x
97 = x
x-intercept is (97, 0)
Sam
Instead you should try and factor it: what two numbers multiply to -99 and add to 2?
Hint: consider the factors of 99
or you could use the time-honored method of "completing the square":
orQuote:
Originally Posted by Devenoor you could use the time-honored method of "completing the square":
as "-1" suggested.
@master
Sorry for the late reply. I have been very busy. Overtime we have went over the four methods for solving quadratic equations(completing the square, square root method, factoring, and quadratic equation), which were taught after the test; (Rofl).
Thank you for replying!