Respuesta :

jcherry99
y = x^2 - 21
The roots occur when y = 0
x^2 - 21 = 0 Add 21 to both sides.
x^2 = 21     Take the square root of both sides.
sqrt(x^2) = sqrt(21)
x = +/-  4.583

I've enclosed a graph to make sure that you can see what the answer means.
Ver imagen jcherry99

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good job