How to find areas of triangles using the formula: A = ½ab×sinC.
Consider a triangle with two sides 'a' and 'b', with angle 'C' between them:
Let side 'a' be the base, then the perpendicular height, 'h' is measured from the top vertex of the triangle, making a 90° angle with the base:
Because 'h' creates a right angled triangle, with 'h' opposite to angle 'C', thenÂ
If you know the base and perpendicular height of a triangle, then you can find the area using this formula:
So in this case, with base = 'a' and perpendicular height = 'bsinC', we have
NOTE: This formula works for any triangle, even when angle 'C' is greater than 90º
Maths Helper Plus can create a
worked solution including a labelled diagram for finding the area of a triangle
using the formula:Â
Step 2Â Display the parameters box
Press the F5 key to display the parameters box:
Click on the 'A' edit box with the mouse, then enter one of the known sides of your triangle.Â
Similarly, click on the 'B' edit box and enter the other known side.
Click on the 'C' edit box, and enter the angle between the two known sides, in degrees.
Click the 'Update' button to refresh the diagram and calculations.
Step 3Â Adjust the scale of the labelled diagram
If the labelled diagram is too large for the screen, then the scale needs to be reduced. Briefly press the F10 key enough times until the entire diagram is visible.
You can make the diagram bigger by holding down 'Ctrl' while you press F10.