Evaluate 1/2a^-4b^2 for a=-2 and b=4
2
1/2
3
4
I got 128. I have a strange feeling that's wrong. So...yeah can someone please explain this?

Question

Evaluate 1/2a^-4b^2 for a=-2 and b=4
2
1/2
3
4
I got 128. I have a strange feeling that's wrong. So...yeah can someone please explain this?

hartnn · Answer

can you show how you got 128 ?
then i'll tell you in which step, there was error.

caitlyn · Answer

I did (-2)^-4 and got 32 then 4^2 and got 16. Then I multiplied those two numbers then divided by 2.

hartnn · Answer

(-2)^-4 = 1/ (-2)^4 = 1/16 
did you get how ?

hartnn · Answer

$$a^{-n} = 1/a^n$$

caitlyn · Answer

No. I don't understand how you got that. Whats the first step?

hartnn · Answer

$$(-2)^{-4} = \dfrac{1}{(-2)^4 }\as, (a)^{-n} = \dfrac{1}{(a)^n }$$
got this ?

caitlyn · Answer

Oh! yeah I forgot you had to do that fraction thing.

hartnn · Answer

$$(-2)^4=[(-2)^2]^2 = 4^2=16$$
$$(-2)^2=(-2)(-2)=4$$

hartnn · Answer

so, now try again, you'll get it :)

caitlyn · Answer

Do you have to do the fraction thing for b?

hartnn · Answer

no, b^2 = 4^2 = 16

caitlyn · Answer

Ok when you do the fraction thing do you multiple the two numbers and then put 1 over fraction? 1/32 or 1/(-2)^-4

caitlyn · Answer

like 1/2x1/(-2)-4x16

caitlyn · Answer

i got 1/2

hartnn · Answer

1/2 is correct :)