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  1. Home
  2. 12th grade
  3. Trigonometry
  4. Exercise : Determine if a triangle is right using the converse of the Pythagorean theorem

Determine if a triangle is right using the converse of the Pythagorean theorem Trigonometry

Determine whether the following triangles are right.

-

We test if the above is a right triangle by plugging the side lengths into the Pythagorean Theorem and checking if the resulting statement is true. That is to say if:

AB^{2} + AC^{2}= BC^{2}

Here we have:

  • BC=9
  • AB=4
  • AC=6

On the one hand:

AB^{2} + AC^{2}= 4^2+6^2=16+36=52

On the other hand:

BC^{2}=9^2=81

We observe that:

AB^{2} + AC^{2}\neq BC^{2}

This is not a right triangle.

-

We test if the above is a right triangle by plugging the side lengths into the Pythagorean Theorem and checking if the resulting statement is true. That is to say if:

AB^{2} + AC^{2}= BC^{2}

Here we have:

  • AB=3
  • BC=4
  • AC=5

On the one hand:

AB^{2} + BC^{2}= 3^2+4^2=9+16=25

On the other hand:

AC^{2}=5^2=25

We observe that:

AB^{2} + BC^{2}=AC^{2}

This is a right triangle.

-

We test if the above is a right triangle by plugging the side lengths into the Pythagorean Theorem and checking if the resulting statement is true. That is to say if:

AB^{2} + AC^{2}= BC^{2}

Here we have:

  • AB=2
  • BC=4
  • AC=6

On the one hand:

AB^{2} + BC^{2}= 2^2+4^2=4+16=20

On the other hand:

AC^{2}=6^2=36

We observe that:

AB^{2} + BC^{2}\neq AC^{2}

This is not a right triangle.

-

We test if the above is a right triangle by plugging the side lengths into the Pythagorean Theorem and checking if the resulting statement is true. That is to say if:

AC^{2} + BC^{2}= AB^{2}

Here we have:

  • AC=7
  • BC=24
  • AB=25

On the one hand:

AC^{2} + BC^{2}= 7^2+24^2=49+576=625

On the other hand:

AB^{2}=25^2=625

We observe that:

AC^{2} + BC^{2}= AB^{2}

This is a right triangle.

-

We test if the above is a right triangle by plugging the side lengths into the Pythagorean Theorem and checking if the resulting statement is true. That is to say if:

AB^{2} + BC^{2}= AC^{2}

Here we have:

  • AB=13
  • BC=5
  • AC=14

On the one hand:

AB^{2} + BC^{2}= 13^2+5^2=169+25=194

On the other hand:

AC^{2}=14^2=196

We observe that:

AB^{2} + BC^{2}\neq AC^{2}

This is not a right triangle.

-

We test if the above is a right triangle by plugging the side lengths into the Pythagorean Theorem and checking if the resulting statement is true. That is to say if:

AB^{2} + AC^{2}= BC^{2}

Here we have:

  • BC=6
  • AB=5
  • AC=\sqrt{11}

On the one hand:

AB^{2} + AC^{2}= 5^2+\sqrt{11}^2=25+11=36

On the other hand:

BC^{2}=6^2=36

We observe that:

AB^{2} + AC^{2}= BC^{2}

This is a right triangle.

-

We test if the above is a right triangle by plugging the side lengths into the Pythagorean Theorem and checking if the resulting statement is true. That is to say if:

AB^{2} + BC^{2}= AC^{2}

Here we have:

  • AB=4
  • BC=4
  • AC=7

On the one hand:

AB^{2} + BC^{2}= 4^2+4^2=16+16=32

On the other hand:

AC^{2}=7^2=49

We observe that:

AB^{2} + BC^{2}\neq AC^{2}

This is not a right triangle.

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See also
  • Course : Right-triangle trigonometry
  • Exercise : Determine lengths in a right triangle using the Pythagorean theorem
  • Exercise : Calculate cos, sin and tan of an angle
  • Exercise : Identify special right triangles
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