What is the value of 1/2^-2x^-3y^5
for x = 2 and y = -4?
16
–4
–1/32
–16

- anonymous

What is the value of 1/2^-2x^-3y^5
for x = 2 and y = -4?
16
–4
–1/32
–16

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- anonymous

Can you make a stab at it or do you need it explained from the start?

- anonymous

i need it explained please...... sorry

- anonymous

No problem! Why don't you start by writing it out using Draw, so I can understand the question better, please?

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## More answers

- anonymous

ok no problem

- anonymous

Great!

- anonymous

|dw:1327955488648:dw|

- anonymous

x = 2 and y = -4? so plug that in

- anonymous

Great, let's do that.

- anonymous

|dw:1327955697547:dw|

- anonymous

and i can do the math with the exponents i just need help on what i do with the 1

- anonymous

Well, show me what you get with thte exponents first

- anonymous

Just the answer's fine, if you think it's right, otherwise we can go through the working if it's wrong

- anonymous

2,048 for the exponents
im not sure what to do with 1

- anonymous

You;re a bit off with the exponents. Let's see your working out. Then we'll get onto the 1.

- anonymous

Let's start with the first bit: What is this? |dw:1327956095456:dw|

- anonymous

-4

- anonymous

Not quite. How do negative exponents work?

- anonymous

im not sure i was sick when ,y teacher explained this to me and this is off my make up work

- anonymous

No problem, I'll explain it to you :D Btw "I don't know" is an excellent answer at any stage, don't be afraid of saying it!

- anonymous

The rule for negative exponents is this:|dw:1327956265582:dw|

- anonymous

Are you familiar with the general rule:|dw:1327956314617:dw| ?

- anonymous

aha ok :) thank you
yeah i am

- anonymous

Well this just takes it a step further. 3^4=81, 3^3=27, 3^2=9, 3^1=3, 3^0=1.

- anonymous

That much you understand already?

- anonymous

yeah i do

- anonymous

Great!

- anonymous

You can see that each time, I reduced the exponent by 1, from 4 to 3 to 2 etc. And the answer got divided by three each time, so from 81 to 27 to 9 to 3 to 1.

- anonymous

Does that make sense?

- anonymous

Or shall I draw it using a picture, if that might help?

- anonymous

yeah i understand what your saying

- anonymous

Great! Then if I take it further, watch what happens: Reducing the exponent by 1, I get 3^-1, and dividing by three on the other side I get 1/3. This continues: 3^-2 = 1/9, 3^-3=1/27 etc. Which is why, as you can see, 3^-x=1/3^x

- anonymous

Did that make sense or should I use draw?

- anonymous

no it made sense i see what your sayinng

- anonymous

Excellent! So now, can you tell me what 2^-2 is?

- anonymous

(Or would you prefer to try the whole question yourself?)

- anonymous

4

- anonymous

Not quite. 2^2=4, so what is 2^-2 ?

- anonymous

-4

- anonymous

Nope, not that either :(

- anonymous

What's the rule we just looked at, for negative exponents?

- anonymous

0.25

- anonymous

|dw:1327957142206:dw|

- anonymous

Did you use your computer's calculator for that or work it out yourself?

- anonymous

See if you can understand the picture I've drawn for you.

- anonymous

i worked it out for myslef

- anonymous

good. how?

- anonymous

calculator :/

- anonymous

THought so :(

- anonymous

im a failure to life
goodbye world im gonna kill myself

- anonymous

The rule for negative indices is this:|dw:1327957460830:dw|

- anonymous

No, don' tdo that!

- anonymous

Look at the rule I've given you, do you understand what I've said?

- anonymous

Ah well, well done for trying :)

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