Step-by-step explanation:
what the other answer tries to say :
you keep the cubic root on one side, and you combine all other terms (here with 5 and 7 only constants) in the other side :
-cubic root(x² - 9) = 2
now we put both sides to the power of 3 and we get
-(x² - 9) = 8
remember, putting a negative number to an odd power (like 3 or 5 or 7 or ...) delivers as result again a negative value.
and now, I think, the other answer made a mistake. that happens, when you don't write down your thoughts.
so,
-(x² - 9) = 8
-x² + 9 = 8
-x² = -1 (and NOT -17)
x² = 1
x = 1 and x = -1
remember, squaring a negative number delivers the same result as squaring the same positive number. therefore, the square root has always 2 solutions : a positive and a negative one.
so, the right answers are the second and the third ones.
