Video: Finding the Perimeter of a Triangle given a Side Length

Find the perimeter of the shape below.


Video Transcript

Find the perimeter of the shape below.

We’re given a triangle that has three equal sides. Each of the sides measures seven and thirty-nine hundredths centimeters. We know that all the sides are equal because of the tick marks labelled on the triangle. We also know, to find the perimeter of a triangle, we add up all the side lengths. In this case, we’ll need to add seven and thirty-nine hundredths plus seven and thirty-nine hundredths plus seven and thirty-nine hundredths. We can line them up vertically, making sure we carefully align the decimal points. From there, we add the units in the hundredths place, nine plus nine plus nine. Nine plus nine plus nine equals 27. We’ll write down our seven and carry over our two. In the tenths place, we’ll then need to add two plus three plus three plus three. Three plus three plus three is nine. And if we add two to that, we have 11. We’ll write one in the tenths place and then carry over the other one from our 11.

In our next step, we’ll need to make sure we remember to bring down the decimal place, and then we can add all the digits in the ones place. One plus seven plus seven plus seven, seven plus seven plus seven is 21. And if you add one to that, you’ll get 22.

The perimeter would be twenty-two and seventeen hundredths. But since we’re measuring a side length, we’ll need to bring down the centimeters. The perimeter of this shape is twenty-two and seventeen hundredths centimeters.

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