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# How does 12x^5 + 5x^6 +1 equal -63 when x= -2? Please explain

1. Watching an exam solutions video on stationary points, and he substitutes x= -2 into y=12x^5 + 5x^6 + 1, which gives him -63 as the value for y.

When I do this is situation though, I get an answer nothing like -63.

I was doing 12(-2^5) + 5(-2^6) + 1, which didn't give me -63. I also tried (12*-2)^5 + (5*2)^6 + 1, which again, didn't give me -63.

Can someone please walk me through how you get y=-63 for the answer of that equation when you substitute x=-2?

Would be a real relief it's been stressing me out all day.

Thanks
2. Well you have 12*(-2)^5 + 5(-2)^6 +1
= 12*-32 +5*64 +1
= -384 + 320 + 1
= -63

(Make sure when you do -2 to a power the -2 is in brackets like (-2)^5 not -2^5
3. (Original post by blobbybill)
Watching an exam solutions video on stationary points, and he substitutes x= -2 into y=12x^5 + 5x^6 + 1, which gives him -63 as the value for y.

When I do this is situation though, I get an answer nothing like -63.

I was doing 12(-2^5) + 5(-2^6) + 1, which didn't give me -63. I also tried (12*-2)^5 + (5*2)^6 + 1, which again, didn't give me -63.

Can someone please walk me through how you get y=-63 for the answer of that equation when you substitute x=-2?

Would be a real relief it's been stressing me out all day.

Thanks
To correctly evaluate it you should be following bidmas rules

So

12(-2)^5+ 5(-2)^6 + 1

-2 to the power of 6 should be a positive result as would any even power (minus x minus = plus) but entering it as you are doing your calculator will work out 2^6 and then make it negative.

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4. If the first '+' was a '-' it works. Typo?

Edit: Whoops. Ignore that!
5. (Original post by Bruhh)
Well you have 12*(-2)^5 + 5(-2)^6 +1
= 12*-32 +5*64 +1
= -384 + 320 + 1
= -63

(Make sure when you do -2 to a power the -2 is in brackets like (-2)^5 not -2^5
If you were doing a positive number, ie 2^5, would the 2 need to be in brackets so it would be (2)^5, or does it only need to be in brackets if its a negative number?
6. (Original post by blobbybill)
If you were doing a positive number, ie 2^5, would the 2 need to be in brackets so it would be (2)^5, or does it only need to be in brackets if its a negative number?
it doesnt need to be but imo its a good idea to put anything you substitute in into brackets
7. (Original post by blobbybill)
If you were doing a positive number, ie 2^5, would the 2 need to be in brackets so it would be (2)^5, or does it only need to be in brackets if its a negative number?
It doesn't need to be, but as mentioned above it's good practice to so you know that the whole part is being raised to the power.
8. Equation
When X = -2
Put take the value of x as - 2 in the given equation

Note:
Even powers of negative numbers = a positive number:
Odd powers of negative numbers = a negative number

12(XX.X.X.X) + 5(X.X.X.X.X.X) = (12 X -32) + (5 X64) + 1= -384 + 320 + 1= -384 + 321= - 6 YAY!!
9. The answer: -63 is correct.
Follow the rules of bidmas. -2^5 is -32. And 2^6 is 64.
-32*12 is -384 + (64*12) +1= 63. Sorry if I'm not being clear i'm typing on my phone.

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