Why can I not use BIDMAS in this integral expression? Edexcel C1 [PLEASE HELP]

C1 Exercise 8F Q5
I found that x = t^3 - t^2 + t + 1

The question asks for when the value of t is 2

So I did 8 - 4 + 2 + 1
Using BIDMAS

8 - (4 + 2 + 1)
= 8 - 8
= 0.
This is wrong, apparently. It is means to be 4 + 2 + 1 after subtraction to total 7.

Why?
Thanks.

Reply 1

nwmyname

OP

13

Original post by SeanFM

8 - 4 + 2 + 1 is not the same as 8 + -1*(4 + 2 + 1) which is actually 8 - 4 - 2 - 1.

Applying BIDMAS to a sum like that isn't really necessary. If you want, do (8-4) + 2 + 1.

So in a level maths, BIDMAS does not apply at all? - at least in integration?

Reply 2

Zacken

22

Original post by nwmyname

So in a level maths, BIDMAS does not apply at all? - at least in integration?

Of course it does apply, you just don't understand it and are using it incorrectly.

Reply 3

techfan42

4

Original post by nwmyname

C1 Exercise 8F Q5
I found that x = t^3 - t^2 + t + 1

The question asks for when the value of t is 2

So I did 8 - 4 + 2 + 1
Using BIDMAS

8 - (4 + 2 + 1)
= 8 - 8
= 0.
This is wrong, apparently. It is means to be 4 + 2 + 1 after subtraction to total 7.

Why?
Thanks.

If you do BIDMAS it should be (8-4) +3 (with solving 2+1 first)

Reply 4

Student403

19

Original post by techfan42

If you do BIDMAS it should be (8-4) +3 (with solving 2+1 first)

Well no, it should be 8 + 2 + 1 first since that's the A in BIDMAS

Reply 5

Kevin De Bruyne

21

Original post by nwmyname

So in a level maths, BIDMAS does not apply at all? - at least in integration?

It can apply anywhere, but how you've used it isn't quite right. If you forget about integration for a second and just consider adding any things a + b - c + d you can't turn that into a + b - (c + d) - if you really were to do that, it would be a + b - (c - d) so that the - next to d cancels out and you've got +d and -c as in the original question.

Reply 6

Good bloke

19

Original post by nwmyname

So I did 8 - 4 + 2 + 1
Using BIDMAS

8 - (4 + 2 + 1)

There's your mistake: you added a fictitious set of parentheses that aren't in the original and that aren't implied by BIDMAS.

Reply 7

HanSoloLuck

2

Original post by nwmyname

C1 Exercise 8F Q5
I found that x = t^3 - t^2 + t + 1

The question asks for when the value of t is 2

So I did 8 - 4 + 2 + 1
Using BIDMAS

8 - (4 + 2 + 1)
= 8 - 8
= 0.
This is wrong, apparently. It is means to be 4 + 2 + 1 after subtraction to total 7.

Why?
Thanks.

I'm no genius or anything, but, doesn't 4 + 2 + 1 = 7.

Reply 8

AstroNandos

21

Original post by nwmyname

C1 Exercise 8F Q5
I found that x = t^3 - t^2 + t + 1

The question asks for when the value of t is 2

So I did 8 - 4 + 2 + 1
Using BIDMAS

BIDMAS can be somewhat misleading, and can make people think division comes before multiplication and addition before subtraction. If you think of division by multiplying by the reciprocal (such as, dividing by 8 is multiplying by 1/8) and subtraction as adding a negative [ 1 - 2 = 1 + (-2) ].

Basically treat division with the same importance as multiplication and do the same for subtraction/addition

so that basically means do 8 - 4 + 2 + 1 from left to right, which is 7

(edited 7 years ago)

Why can I not use BIDMAS in this integral expression? Edexcel C1 [PLEASE HELP]

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