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Kids Math

Pythagorean Theorem

Skills needed:
  • Multiplication
  • Exponents
  • Square root
  • Algebra
  • Angles
The Pythagorean Theorem helps us to figure out the length of the sides of a right triangle. If a triangle has a right angle (also called a 90 degree angle) then the following formula holds true:

a2 + b2 = c2


Where a, b, and c are the lengths of the sides of the triangle (see the picture) and c is the side opposite the right angle. In this example, c is also called the hypotenuse.

Let's work through a few examples:

1) Solve for c in the triangle below:

In this example a = 3 and b=4. Let's plug those into the Pythagorean Formula.

a2 + b2 = c2

32 + 42 = c2

3x3 + 4x4 = c2

9+16 = c2

25 = c x c

c = 5


2) Solve for a in the triangle below:

In this example b=12 and c= 15

a2 + b2 = c2

a2 + 122 = 152

a2 + 144 = 225

Subtract 144 from each side to get:

144 - 144 + a2 = 225 - 144

a2 = 225 - 144

a2 = 81

a = 9


The Pythagorean Theorem itself

The theorem is named for a Greek mathematician named Pythagoras. He came up with the theory that helped to produce this formula. The formula is very useful in solving all sorts of problems.

Here is what the theorem says:

In any right triangle, the area of the square whose side is the hypotenuse (remember this is the side opposite the right angle) is equal to the sum of the areas of the squares whose sides are the two legs (the two sides that meet at a right angle).

This may not make a lot of sense when you first read it. Let's show more what the formula does and what the words say in a picture.

If you take each side of the yellow triangle and use it to make a square (see the picture below). Then you get these three squares. The area of each square is width x height. So in this example the area of each square is a2, b2, and c2.



What the theorem says is that the area of the purple square plus the area of the blue square will equal the area of the green square. That's the same as saying:

a2 + b2 = c2

Advanced Kids Math Subjects

Statistics
Mean, Median, Mode, and Range
Picture Graphs

Algebra
Order of Operations
Exponents
Ratios
Ratios, Fractions, and Percentages

Geometry
Polygons
Quadrilaterals
Triangles
Pythagorean Theorem
Circle
Perimeter
Surface Area

Misc
Prime Numbers
Roman Numerals

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1952 Mr. T (Actor)
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