How do you determine the x-intercepts of the polynomial function y = -(2x+5)^3 - 20
I did this:
0 = -(2x+5)^3 - 20
20 = -2x+5)^3
-5 3sqrt(20/-2) (3 before the sqrt being the little 3)
x= 10.7
The answer should be -3.86 however.
You've dropped a "(". It should be 20= -(2x+5)^3. Now "undo" that. -20^{1/3}= 2x+ 5
2x= -20^{1/3}- 5, x= (-20^{1/3})/2
"cube root" or "cbrt" not "square root" nor "3sqrt"-5 3sqrt(20/-2) (3 before the sqrt being the little 3)
But your real error is that you divided by two before taking the cuberoot. You must take the cuberoot first because the "2x+ 5" is inside the cube.
x= 10.7
The answer should be -3.86 however.