Lesson: The Converse of the Pythagorean Theorem

In this lesson, we will learn how to use the converse of the Pythagorean theorem to determine whether a triangle is a right triangle.

Sample Question Videos

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Worksheet: The Converse of the Pythagorean Theorem • 24 Questions • 6 Videos

Q1:

What can the converse of the Pythagorean theorem be used for?

Q2:

Can the lengths 7.9 cm, 8.1 cm, and 5.3 cm form a right-angled triangle?

Q3:

Is 𝐴 𝐶 𝐷 a right-angled triangle at 𝐶 ?

Q4:

A triangle has sides of lengths 36.4, 27.3 and 45.5. What is its area?

Q5:

The Pythagorean theorem states that, in a right triangle, the area of a square on the hypotenuse is equal to the sum of the areas of the squares on the legs. Does this mean that a triangle where 𝑐 = 𝑎 + 𝑏 2 2 2 is necessarily a right triangle?

Let us assume that 𝐴 𝐵 𝐶 is of side lengths 𝑎 , 𝑏 , and 𝑐 , with 𝑐 = 𝑎 + 𝑏 2 2 2 . Let 𝐷 𝐵 𝐶 be a right triangle of side lengths 𝑎 , 𝑏 , and 𝑑 .

Using the Pythagorean theorem, what can you say about the relationship between 𝑎 , 𝑏 , and 𝑑 ?

We know that for 𝐴 𝐵 𝐶 , 𝑐 = 𝑎 + 𝑏 2 2 2 .

What do you conclude about 𝑑 ?

Is it possible to construct different triangles with the same length sides?

What do you conclude about 𝐴 𝐵 𝐶 ?

Q6:

In triangle point lies on and , , , and . Find the length of to the nearest tenth, and then determine whether is a right-angled triangle or not.

Q7:

In triangle 𝐴 𝐵 𝐶 , let 𝐷 on 𝐵 𝐶 be the foot of the altitude from 𝐴 . If 𝐴 𝐶 = 1 1 8 . 9 , 𝐴 𝐷 = 6 9 . 6 1 8 , and 𝐵 𝐷 = 5 0 . 9 4 , is 𝐴 𝐵 𝐶 right angled at 𝐴 ?

Q8:

In triangle 𝐴 𝐵 𝐶 , 𝐴 𝐷 is perpendicular to 𝐵 𝐶 , 𝐷 lies between 𝐵 and 𝐶 , 𝐵 𝐷 = 8 , 𝐶 𝐷 = 2 , and 𝐴 𝐷 = 4 . Is 𝐴 𝐵 𝐶 a right-angled triangle?

Q9:

What does ( 𝐴 𝐶 ) 2 equal to?

Q10:

In the figure shown, suppose that 𝐴 𝐸 = 2 𝐵 𝐶 and 𝐵 𝐷 = 8 . Determine 𝐴 𝐷 and 𝐸 𝐷 rounded to the nearest hundredth, if necessary.

Q11:

Is 𝐸 𝐴 𝐷 a right-angled triangle at 𝐴 ?

Q12:

𝐴 𝐵 𝐶 is a triangle where 𝐴 𝐵 = 3 c m , 𝐵 𝐶 = 4 c m and 𝐴 𝐶 = 5 c m . Find the size of 𝐴 𝐵 𝐶 .

Q13:

𝐴 𝐵 𝐶 is a triangle where 𝐴 𝐵 = 𝐴 𝐵 = 5 c m , 𝐵 𝐶 = 1 2 c m and 𝐴 𝐶 = 1 3 c m . Find the size of 𝐴 𝐵 𝐶 .

Q14:

Two lines intersect at the point 𝐴 ( 0 , 1 ) . One line goes through the point 𝐵 ( 2 , 3 ) , and the other goes through the point 𝐶 ( 2 , 1 ) .

Find the lengths of 𝐴 𝐵 , 𝐴 𝐶 , and 𝐵 𝐶 .

Using the Pythagorean theorem, decide: is triangle 𝐴 𝐵 𝐶 a right triangle?

Are the two lines perpendicular?

Q15:

Two lines intersect at the point 𝐴 ( 3 , 1 ) . One line goes through the point 𝐵 ( 5 , 1 ) , and the other goes through the point 𝐶 ( 2 , 6 ) .

Find the lengths of 𝐴 𝐵 , 𝐴 𝐶 , and 𝐵 𝐶

Using the Pythagorean theorem, decide: is triangle 𝐴 𝐵 𝐶 a right triangle?

Hence, are the two lines perpendicular?

Q16:

In rectangle 𝐴 𝐵 𝐶 𝐷 , suppose 𝐴 𝐸 = 8 , 𝐷 𝐸 = 2 , and 𝐷 𝐶 = 4 . Is 𝐵 𝐸 𝐶 right angled?

Q17:

In the isosceles triangle 𝐴 𝐵 𝐶 below, 𝐴 𝐷 = 8 6 . 4 c m , 𝐵 𝐶 = 1 2 9 . 6 c m , and 𝐴 𝐸 = 1 4 7 . 6 c m . Is 𝐵 𝐴 𝐸 a right-angled triangle?

Q18:

Can the lengths 16.6 cm, 6.3 cm, and 11.3 cm form a right-angled triangle?

Q19:

Can the lengths 14.4 cm, 19.2 cm, and 24 cm form a right-angled triangle?

Q20:

Is 𝐴 𝐶 𝐷 a right-angled triangle at 𝐶 ?

Q21:

Is 𝐴 𝐶 𝐷 a right-angled triangle at 𝐶 ?

Q22:

A triangle has sides of lengths 20.4, 59.5 and 62.9. What is its area?

Q23:

A triangle has sides of lengths 44, 4.2 and 44.2. What is its area?

Q24:

In triangle point lies on and , , , and . Find the length of to the nearest tenth, and then determine whether is a right-angled triangle or not.

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