# Tag: secondary 3 maths tuition

## A Maths Tuition: Trigonometry Formulas

Many students find **Trigonometry in A Maths challenging**.

This is a **list of Trigonometry Formulas** that I compiled for A Maths. Students in my A Maths tuition class will get a copy of this, neatly formatted into one A4 size page for easy viewing.

**A Maths: Trigonometry Formulas**

;

;

**Special Angles:**

Amplitude: ; Period:

Amplitude: ; Period:

Period:

Area of

**Sine Rule:**

**Cosine Rule:**

## Challenging Geometry E Maths Question — St Andrew’s Sec 3 Maths Tuition Question

**Question:**

ABCD is a rectangle. M and N are points on AB and DC respectively. MC and BN meet at X. M is the midpoint of AB.

(a) Prove that and are similar.

(b) Given that area of : area of =9:4, find the ratio of,

(i) DN: NC

(ii) area of rectangle ABCD: area of . **(Challenging)**

**[Answer Key]** (b) (i) 1:3

(ii) 20:3

**Suggested Solutions:**

(a)

(vert. opp. angles)

(alt. angles)

(alt. angles)

Therefore, and are similar (AAA).

(b) (i)

Let and

Then

So

Thus,

(ii)

**We now have a shorter solution, thanks to a visitor to our site! (see comments below)**

From part (a), since and are similar, we have

This means that

Thus (the two triangles share a common height)

Now, note that

Hence area of

We conclude that area of rectangle ABCD: area of

Here is a longer solution, for those who are interested:

Let area of

Let area of

Let area of

We have since and have the same base BC and their heights have ratio 3:2.

Cross-multiplying, we get

So

since and have the same base BC and their heights have ratio 3:4.

Hence,

Thus, area of

area of rectangle ABCD: area of =40:6=20:3