Find X in a Right Triangle: Given Sides 5 and 12

Triangle Analysis with Missing Angle Information

Look at the following triangle.

555121212XXX

What is the value of X?

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1

Understand the problem

Look at the following triangle.

555121212XXX

What is the value of X?

2

Step-by-step solution

It is important to remember: the Pythagorean theorem is only valid for right-angled triangles.

This triangle does not have a right angle, and therefore, the missing side cannot be calculated in this way.

3

Final Answer

Cannot be solved

Key Points to Remember

Essential concepts to master this topic
  • Rule: Pythagorean theorem only applies to right triangles
  • Technique: Check for right angle marking or 90° symbol first
  • Check: Without angle information, side lengths alone cannot determine triangle type ✓

Common Mistakes

Avoid these frequent errors
  • Assuming all triangles can use Pythagorean theorem
    Don't automatically apply a² + b² = c² to any triangle = wrong answers! The Pythagorean theorem only works for right triangles with a 90° angle. Always verify the triangle has a right angle before using this formula.

Practice Quiz

Test your knowledge with interactive questions

Consider a right-angled triangle, AB = 8 cm and AC = 6 cm.
Calculate the length of side BC.

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FAQ

Everything you need to know about this question

How can I tell if a triangle is a right triangle?

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Look for a right angle symbol (small square) in one of the corners, or check if one angle measures exactly 90 degrees. Without this marking, you cannot assume it's a right triangle.

What if the triangle looks like it has a right angle?

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Never assume based on appearance alone! Diagrams can be misleading. You need either an explicit right angle marking or given angle measurements to confirm it's 90°.

Are there other ways to find the missing side?

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Yes! You can use the Law of Cosines or Law of Sines, but these require knowing at least one angle measurement. With only two sides given, the problem cannot be solved.

Why can't this triangle be solved with just two sides?

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Because infinitely many triangles can have the same two side lengths! Without knowing an angle, you cannot determine the unique shape of the triangle.

What should I do when a triangle problem cannot be solved?

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Choose "Cannot be solved" as your answer. It's perfectly valid in mathematics to recognize when insufficient information is given!

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