Lesson video

Hello.

My name is Mr Clasper and today we're going to be constructing triangles.

We're going to draw this triangle accurately.

This is an SAS triangle.

This stands for side angle side, and this is when we have an angle subtended between two sides which we know the length of.

Let's begin by drawing the base of our triangle which is 10 centimetres.

We then need to measure a 37 degree angle from the left of the line.

Remember in this case, you're using the inside scale of the protractor.

Make sure also that the crosshair of the protractor is at the end of the line.

Make a mark at 37 degrees.

And then we're going to line our ruler with the end of the base of our triangle on the mark we just made.

And we're going to draw a four centimetre line.

Our last step is to join this to finish off our triangle.

Now we should have a triangle with a side of 10 and four centimetres and an angle of 37.

In this example, we're going to draw an ASA triangle.

This stands for angle side angle.

We can draw one of these when we have a side length which we know, and two angles using this side.

Let's draw our base again.

This is 10 centimetres.

We then need to use our protractor, and we're going to measure a 53 degree angle from the left and make a mark.

Then we're going to make a 37 degree angle from the right, and we can join these up.

Notice that the lines have crossed at the top of our triangle.

These are fine, and these are often referred to as construction lines.

Our triangle is here, and we should have a 53 degree angle and a 37 degree angle.

Here's some questions for you to try.

Pause the video to complete your task and click resume once you're finished.

And here are your solutions.

So the best way to check if your diagrams are correct is to make sure they have the lengths and angles indicated.

In this example, we're going to make an SSS triangle.

This stands for side side side, and it's where we know all three sides of a triangle.

We know the base is 10 centimetres, and for the other two sides we're going to need a compass.

With your compass, we can measure five centimetres, and then keeping the compass at this distance, we can place the point on the left side of our line and we're going to create a curve.

We're then going to take our compass and measure 7.

8 centimetres.

Then we're going to put the point of our compass on the other side of our line, and make a curve.

Where our two curves meet will be one of the varieties of our triangle.

So we're going to join lines to this intersection.

Now we have a triangle which has side lengths of 10 centimetres, five centimetres, and 7.

8 centimetres.

In this example, we're going to draw an RHS triangle.

This stands for right angle, hypotenuse and side.

This is where we have a right angle triangle and we know the length of the hypotenuse and the side.

If we have these pieces of information, we can draw the triangle accurately.

Let's draw our base first.

The base is eight centimetres.

We then need to make sure we have a 90 degree angle.

So we're going to make a mark at 90 degrees and draw a line.

Don't worry how long this line is, as we can use this as a construction line.

For the last length, we need to measure 10 centimetres with our compass.

Place the point on the right side of our base and make a curve.

We can then draw a line from the right side of our base to the point where our arc intercepts the length, which is the height of our triangle.

We now have a triangle with a right angle, a base of eight, and a hypotenuse of 10 centimetres.

Here's some questions for you to try.

Pause the video to complete your task and click resume once you're finished.

And here are your solutions.

So once again to check your work, just make sure that your triangles have the same dimensions as these ones.

And that is the end of our lesson on constructing triangles.

Want to give the exit quiz a go just to boost your knowledge further.

I'll hopefully see you soon.