Expressing the volume and area in terms of x and y???

I always have trouble with these types of questions where you have to express the volume and area in terms of x and y!! This is definitely one of the questions I struggle on the most. Below is an example of the type of questions I get stuck on. Are there any good video tutorials on YouTube about these types of questions? (I've already checked the tutorials on Exam Solutions but only basic examples are given). Someone please help me :frown:

Click to enlarge picture below...
Expressing the Volume and Area.png

Reply 1

DylanJ42

18

Original post by Philip-flop

I always have trouble with these types of questions where you have to express the volume and area in terms of x and y!! This is definitely one of the questions I struggle on the most. Below is an example of the type of questions I get stuck on. Are there any good video tutorials on YouTube about these types of questions? (I've already checked the tutorials on Exam Solutions but only basic examples are given). Someone please help me :frown:

Click to enlarge picture below...
Expressing the Volume and Area.png

just use the formula of the volume of a trapezium and then multiply in by the "thickness" of the shape (which is y) and set it equal to 900

Edit; nevermind i misunderstood the shape

Edit 2: ... its actually fine, the advice is okay

(edited 8 years ago)

Reply 2

Zacken

22

Original post by Philip-flop

...

The area of a rectangle is the width multiplied by the height, this holds even if they are functions of

x

and/or

y

. :-)

Reply 3

ComputerMaths97

17

Original post by Philip-flop

I always have trouble with these types of questions where you have to express the volume and area in terms of x and y!! This is definitely one of the questions I struggle on the most. Below is an example of the type of questions I get stuck on. Are there any good video tutorials on YouTube about these types of questions? (I've already checked the tutorials on Exam Solutions but only basic examples are given). Someone please help me :frown:

Click to enlarge picture below...
Expressing the Volume and Area.png

When I first started practicing them, I just replaced x and y with simple values. Then, every time I did a calculation with them, I left it as multiples of these values (I also circled the values). It meant I was doing normal maths, then at the end just rub out all the values and replace with x's and y's.

Reply 4

Philip-flop

OP

18

Original post by Zacken

The area of a rectangle is the width multiplied by the height, this holds even if they are functions of

x

and/or

y

. :-)

Yeah that's true. But I got stuck on how to work out the cross-sectional area of the trapezium and had trouble working out the length of the sloping sides (took me ages to figure out that I needed to use the Sine rule).

I'm slowly starting to realise that I'm no where near ready for my exams in the summer :frown:

Reply 5

Philip-flop

OP

18

Original post by ComputerMaths97

When I first started practicing them, I just replaced x and y with simple values. Then, every time I did a calculation with them, I left it as multiples of these values (I also circled the values). It meant I was doing normal maths, then at the end just rub out all the values and replace with x's and y's.

I too find myself doing that! It is a great technique to learn, but I worry I won't have time for things like that if I stumble across some difficulty in the exams :frown:

Reply 6

ComputerMaths97

17

Original post by Philip-flop

I too find myself doing that! It is a great technique to learn, but I worry I won't have time for things like that if I stumble across some difficulty in the exams :frown:

With practice you'll learn. Once you fully get your head around the idea that algebra is just a letter representing a number, and therefore nothing changes at all, you'll be fine.

Reply 7

Philip-flop

OP

18

Does anyone know the proper name for these types of questions? It's definitely something I need to practice but Only come across these past paper questions every so often :frown:

Reply 8

Notnek

21

Original post by Philip-flop

Does anyone know the proper name for these types of questions? It's definitely something I need to practice but Only come across these past paper questions every so often :frown:

They are usually part of a topic titled "Solving problems using turning points" or something similar.