The area is the size of the surface and states the number of unit squares needed to completely cover that surface.

The sine of an angle (sin(θ°)) is the y-coordinate of point P on the triangle formed inside the unit circle.

Calculating the area of any triangle when the height is not known

Maths

Checking and securing understanding of trigonometric ratios

Drawing the sine and cosine graphs

Drawing the tangent graph

Interpreting the trigonometric graphs

The area of any triangle

The sine rule

The cosine rule

Using the sine and cosine rules

Considering the appropriate trigonometric rule

Problem solving with non right-angled trigonometry

In the prior unit, pupils explored the trigonometric ratios for right-angled triangles in a variety of situations. In this unit, pupils explore what can be done when we have a triangle that is not right-angled.

In this unit, pupils explore how to apply knowledge in trigonometry to non right-angled triangles.

Non right-angled trigonometry

A right-angled triangle has a height of 12 cm and a hypotenuse of 15 cm. The area of the triangle is {{}}cm$$^2$$.

An isosceles triangle has lengths 26 cm, 26 cm and 20 cm. The area of the isosceles triangle. is {{}}cm$$^2$$.

A triangle is drawn. The adjacent lengths are 7 cm and 9 cm with a 47° angle in between. The area of the triangle, to 1 decimal place, is {{}}cm$$^2$$.

An equilateral triangle has lengths of 6 cm. The area of the triangle, to 1 decimal place, is {{}}cm$$^2$$.

Two adjacent lengths of a triangle are $$x$$ cm and 6 cm with a 47° angle in between. The area is 26.3 cm$$^2$$. Work out the value of $$x$$ , giving your answer rounded to the nearest integer. 

An equilateral triangle with lengths of $$x$$ cm is drawn. It has an area of 3.9 cm$$^2$$. Work out the length of the equilateral triangle, giving your answer as a whole number. 

A triangle with perpendicular height =  5  cm and base = 6  cm

A triangle with perpendicular height =  11  cm and base = 4  cm

A triangle with perpendicular height =  4  cm and base = 8  cm

A triangle with perpendicular height =  3  cm and base = 3  cm

Match the areas of these triangles with their dimensions. 

$$\frac{1}{2}\times 6.3\times5\times\text{sin}(55.3°)$$

$$\frac{1}{2}\times 6.3\times5.4\times\text{sin}(49.8°)$$

$$\frac{1}{2}\times 5.4\times5\times\text{sin}(74.9°)$$

$$\frac{1}{2}\times 6.3\times5.4\times\text{sin}(55.3°)$$

$$\frac{1}{2}\times 5.4\times5\times\text{sin}(55.3°)$$

Which of the following calculate the area of this triangle?

The area of this triangle, given to 2 significant figures, is {{}}cm$$^2$$.

A right angled triangle has a height of 12 cm and a hypotenuse of 13 cm. Work out the area.

Six equilateral triangles are put together to make a regular hexagon. The length of each triangle is 3 cm. Work out the exact area of the regular hexagon. 

An isosceles triangle has a base of 4 cm and base angles of 68.2°. Select the correct area given to 2 significant figures. 

This lesson was made for home learning during the pandemic.

Calculating the area of any triangle when the height is not known

Lesson outcome

This lesson was made for home learning during the pandemic.