Edexcel Maths C1 may 2014 help!

Okay so I've been working through past papers and this one is pretty simple but on question 10)b) I swear it doesn't make any sense?

You have to find the normal to a curve, and you have already got the differentiated equation, so you only have to substitute in the x value to get the gradient of the tangent etc.etc.

but f'(4)=3/8 * 4² - 10 * 4^-1/2 +1
=3/8 * 16 - 10 * 1/2 +1
=48/8 - 5 + 1
=6 - 5 + 1
which is where the problem is because in bidmas you do addition then subtraction which would suggest = 0 because 6- (5+1) as addition first.
however in the markscheme it says =2 which would be (6-5)+1

Where am I going wrong? should i not follow bidmas?

Reply 1

davros

16

Original post by AristotleAxolotl

Okay so I've been working through past papers and this one is pretty simple but on question 10)b) I swear it doesn't make any sense?

You have to find the normal to a curve, and you have already got the differentiated equation, so you only have to substitute in the x value to get the gradient of the tangent etc.etc.

but f'(4)=3/8 * 4² - 10 * 4^-1/2 +1
=3/8 * 16 - 10 * 1/2 +1
=48/8 - 5 + 1
=6 - 5 + 1
which is where the problem is because in bidmas you do addition then subtraction which would suggest = 0 because 6- (5+1) as addition first.
however in the markscheme it says =2 which would be (6-5)+1

Where am I going wrong? should i not follow bidmas?

Bidmas doesn't say any such thing!

Addition and subtraction have equal priorities, so you carry out the operations reading from left to right.

Therefore 6 - 5 + 1 = 1 + 1 = 2

Reply 2

beast709

2

You can't just put down 6 - 5 + 1 as 6 -(5+1) because if you expand the bracket by multiplying with the negative, you get 6 -5 -1 which is not the same as 6-5+1.

Reply 3

AristotleAxolotl

OP

1

Really? I could have sworn I was taught they also have priorities.
Are multiplication and division equal then as well?

Reply 4

davros

16

Original post by AristotleAxolotl

Really? I could have sworn I was taught they also have priorities.
Are multiplication and division equal then as well?

Multiplication and division have equal priorities too, so if you just have mutliplications and divisions in sequence you perform them from left to right. However, multiplication and division take priority over addition and subtraction.

Reply 5

haaris28

6

Original post by AristotleAxolotl

Really? I could have sworn I was taught they also have priorities.
Are multiplication and division equal then as well?

In bidmass, multiplication and division have higher priorities than addition and subtraction.
In cases where it is only addition and subtraction, the sum must be done from left to right.
In cases where it is only multiplication and subtraction, order doesn't matter.
In cases it is all four functions, multiplication and division must be done first, and then addition and subtraction.

so in your case 6 - 5 +1 = 1 + 1 = 2 because your going from left to right. you could write it as (6-5) +1 to make it easier.
brackets have the highest priority.

Edexcel Maths C1 may 2014 help!

Quick Reply

Related discussions

Latest

Trending

Trending

Articles for you