Tuition given in the topic of

E-Maths Tuition Questions from the tuition centre desk of

Miss Loi at

5:39 pm (Singapore time)

Today’s question looks sooo simple. Just punch those keys on your state-of-the-art Casio scientific calculator and you will get it right … except that this is a Paper 1 question and your favourite Casio calculator should not be there!

So how now? Go ask your Grandma (Ah *SOH*) with the big foot (*TOA CAH)* for help *lah*!

In the diagram, a ladder BC is leaning against the wall AD. Given that, sin `x` = 5/13. Find the cosine of angle DCB.

### Revision Exercise

To show that you have understood what Miss Loi just taught you from the centre, you *must*:

## 2 Comments

曜

日

sin x = 5/13 => sin ABC = 5/13 => cos BCA = 5/13 => cos DCB = -5/13.

曜

日

Great stuff Nick!

The purpose of this question is to remind students that the standard trigo ratios (i.e. TOA CAH SOH -> Tan: Opp/Adj; Cos: Adj/Hypo; Sin: Opp/Hypo) applies only to an

acuteangle.In order to solve for angle DCB which is an

obtuseangle in the question, students need to remember a further set of equations i.e:sin θ = sin (180

^{o}- θ)cos θ = -cos (180

^{o}- θ)tan θ = -tan (180

^{o}- θ)Hence exam questions usually require multiple steps like these. If everyday just simply TOA CAH SOH TOA CAH SOH, the examination board can close shop

liao!So remember this well!