You are Here: Home >< Maths

# MAT question help watch

1. I dont understand how to do this question/solution:

QP
https://s3-eu-west-1.amazonaws.com/w...3f43f7a3_1.pdf

Ans:
https://s3-eu-west-1.amazonaws.com/w...dc24cd54_1.pdf

- How did they know that the middle sector of A was at a degree of 90 even though it can be seen from the diagram that isnt always correct..
- I dont understand how they've worked out the area of the triangle and the placement of theta also confuses me

If anyone wants to help me by solving it you're most welcome
2. (Original post by Carman3)
- How did they know that the middle sector of A was at a degree of 90 even though it can be seen from the diagram that isnt always correct..
- I dont understand how they've worked out the area of the triangle and the placement of theta also confuses me

If anyone wants to help me by solving it you're most welcome
Question 4 part (ii) in case anyone else want to look.

Angle subtended by middle sector is 90 because, angle to the left is theta, and angle to the right is 90 - theta, and since the total is 180, the remainder - the sector's angle - is 90.

Since the radius of the circle is "1", then the x co-ordinates of -cos theta and sin theta, imples the angles marked are theta.
Triangles are congruent, having two sides next to the right angle of cos theta and sin theta, hence the area formula used. (1/2) base times height, and times 2 as there are two identical triangles.
3. (Original post by ghostwalker)
Question 4 part (ii) in case anyone else want to look.

Angle subtended by middle sector is 90 because, angle to the left is theta, and angle to the right is 90 - theta, and since the total is 180, the remainder - the sector's angle - is 90.

Since the radius of the circle is "1", then the x co-ordinates of -cos theta and sin theta, imples the angles marked are theta.
Triangles are congruent, having two sides next to the right angle of cos theta and sin theta, hence the area formula used. (1/2) base times height, and times 2 as there are two identical triangles.
How is angle to the left theta and angle to the right 90-theta. I also dont get the co-ordinates bit like how can you put -cos and sin on the same x axis
4. (Original post by Carman3)
How is angle to the left theta and angle to the right 90-theta.
For the left.
Since the x-coordinate is -cos theta, and the semicicle has radius 1, then that's the value you'd get if the angle to the left was theta. Hence the angle is theta. No other value in the range 0 to 90 will do.

For the right.
Similar argument for the angle theta, and hence the angle at the origin is 90-theta.

I also dont get the co-ordinates bit like how can you put -cos and sin on the same x axis
I don't see your problem really. You're given the two coordinates, and they happen to be function of theta. Their actual position is going to depend on what theta is. We can't say, for example, that one is between 0.4 and 0.5, only that it is somewhere between 0 and 1.
5. (Original post by ghostwalker)
For the left.
Since the x-coordinate is -cos theta, and the semicicle has radius 1, then that's the value you'd get if the angle to the left was theta. Hence the angle is theta. No other value in the range 0 to 90 will do.

For the right.
Similar argument for the angle theta, and hence the angle at the origin is 90-theta.

I don't see your problem really. You're given the two coordinates, and they happen to be function of theta. Their actual position is going to depend on what theta is. We can't say, for example, that one is between 0.4 and 0.5, only that it is somewhere between 0 and 1.
oh right
I was trying to look at the question in terms of sine curve and cos curve

### Related university courses

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: October 30, 2016
The home of Results and Clearing

### 2,495

people online now

### 1,567,000

students helped last year
Today on TSR

### GCSE results day guidance

All you need to know is here

### University open days

1. Bournemouth University
Wed, 22 Aug '18
2. University of Buckingham
Thu, 23 Aug '18
3. University of Glasgow
Tue, 28 Aug '18
Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams