CAIE IGCSE Mathematics Sine Cosine and Tangent Ratios

Use SOHCAHTOA to choose sine, cosine or tangent from a right-angled triangle, then calculate an acute angle or missing side and round the final answer correctly.

Exam points

label opposite, adjacent and hypotenuse relative to the stated acute angle before choosing a ratio
use sin = opposite/hypotenuse, cos = adjacent/hypotenuse or tan = opposite/adjacent
apply an inverse trigonometric function for an angle and round only the final result as instructed

[Maximum number: 3]

The diagram shows a circle, centre O, radius 11 cm. C, F, G and H are points on the circumference of the circle.
The line AD touches the circle at C and is parallel to the line EG. B is a point on AD and angle $A B O=140^{\circ}$ .

Show that $BC=13.11\text{ cm}$ , correct to 2 decimal places.

180-140 or 90- their (b)(ii)
$\tan(180-140)=\frac{11}{BC}$ oe
$[BC=]13.109\ldots$

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C6.2.1 Know and use the sine, cosine and tangent ratios for acute angles in question 1