GCSE Secondary Maths Age 13-17 - Pythagoras & Trigonometry: Cosine Rule - Explained

The video tutorial explains how to solve a triangle problem without a right angle using the sine and cosine rules. It begins by identifying the given data, including the triangle's area and an angle. The instructor demonstrates how to use the area formula to find the length of side BC, emphasizing the importance of maintaining accuracy by not rounding off early. The cosine rule is then applied to find the unknown side, with detailed steps on using a calculator correctly. The tutorial concludes with a discussion on rounding the final answer to three significant figures and the allocation of marks for each step.

What type of triangle is being discussed in the problem?

• Isosceles triangle

• Equilateral triangle

• Right-angled triangle

• Scalene triangle

Which formula is used to calculate the area of the triangle in this problem?

• Base times height divided by two

• 1/2 AB sine C

• Pythagorean theorem

• Heron's formula

What is the calculated length of BC before rounding?

• 38.00

• 37.0410434967

• 37.04

• 36.00

Why is it important not to round off early in calculations?

• It prevents loss of accuracy marks

• It makes calculations easier

• It helps in understanding the problem better

• It saves time

In which situation is the cosine rule used?

• When you have a right-angled triangle

• When you have three known sides

• When you have an equilateral triangle

• When you have two angles and one side

What is the final length of AB rounded to three significant figures?

• 31.00 meters

• 31.07 meters

• 30.00 meters

• 31.08 meters

How many marks are awarded for correctly using the cosine rule?

• Four marks

• Three marks

• Two marks

• One mark