Question

Please help which one is it!!

Answer 1

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.

Answer 2

Last one and first. You can find out why by isolating the cube root and cubing both sides.