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Started by turbodante on Sep 28, 2021 7:29:44 PM
y=2x²-5x-1

Can anyone show me how to arrive at y =17 when X = -2

Seems that my GCSE Bodmas is failing me. I keep getting y= 1

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turbodante - 28 Sep 2021 19:38:28 (#1 of 15)

y = 2(-2)²-5(-2)-1

y = 2(-4)-5(-2)-1

y = -8+10–1

y = 1

turbodante - 28 Sep 2021 19:39:18 (#2 of 15)

But that is not what the graph does. The graph is y = 17 when X = -2.

Arjuna - 28 Sep 2021 20:42:32 (#3 of 15)

Minus two squared is not minus four

dreams99 - 28 Sep 2021 20:42:36 (#4 of 15)

You have your first term wrong. (-2)^2 is 4, not -4.

So the first term is 8, not -8. which is your 16 difference.

kvelertak - 28 Sep 2021 19:44:06 (#5 of 15)

y = 2(4)-(-10)-1

turbodante - 28 Sep 2021 19:46:40 (#6 of 15)

Arghh. Thank you. It's been a while since I did maths with pen and paper.

Arjuna - 28 Sep 2021 20:51:56 (#7 of 15)

The rules have changed since then

Dementor - 28 Sep 2021 21:04:48 (#8 of 15)

It’s that bloody “.” notation the Yanks use for multiplication that confuses me.

NightInTGeorgia - 28 Sep 2021 21:07:28 (#9 of 15)

Not just the yanks. Was standard at university 40 years ago.

NightInTGeorgia - 28 Sep 2021 21:08:37 (#10 of 15)

x is confusing algebraically if you are using x as a variable. Which you start to write as back to back C’s

Dementor - 28 Sep 2021 21:08:56 (#11 of 15)

We only used it for vector dot products, I think.

NightInTGeorgia - 28 Sep 2021 21:09:33 (#12 of 15)

Hang on you might be right

turbodante - 28 Sep 2021 20:57:40 (#13 of 15)

Yes, the X used to confuse me no end.

Also took me ages to understand what to do with to the terms when moving them over the other side of the equals sign.

dreams99 - 28 Sep 2021 22:10:49 (#14 of 15)

Just do it the slow way. Add things to both sides, or subtract/multiply/divide to eliminate the term on one side and bring it yo the other.

Tomnoddy - 28 Sep 2021 23:04:36 (#15 of 15)

Changing the side, changing the sign is the way I was taught to think of it. It was a crap way of teaching it.

The modern way is, or should be, to perform the same mathematical step on each side and see where it takes you. Well, in a general sense that is.

However, it doesn't really come into the equation above.

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