Question

Solve and check.
7 ^-x = 21

Answer 1

I think you have to use log(x), so:
-x log(7)=log(21)
-x = log(21)/log(7)
X = -(log(21)/log(7))

Answer 2

The answers are
-2.687
-1.565
-3.729
-1.125

Answer 3

I just dont understand how to get the answer

Answer 4

just use calculator & find value of log(21) & log(7) & plug that values in last step
You will get the answer

Answer 5

& simplify it

Answer 6

If you want to take down the -x from 7^-x, you need to logarithm it, so:
7^-x (use log) ---> -x*log (7)
But if you make a change at the left side of the equal mark (=), then you have to do it on the right side too. So 21 (use log) ---> log(21)

Answer 7

Do I divide?

Answer 8

the first answer is good. try to understand each steps.
however for the answer, indeed, it's just \(-\log(21)/\log(7)\) to enter in the calculator.
I obtain -1.565

Answer 9

After you log each side of the equation, you want to make x by itself, so you throw over the log(7) to the other side.