PYTHAGOREAN THEOREM. Pythagorean Theorem. Over 2,500 years ago, a Greek mathematician named Pythagoras developed a proof that the relationship between the hypotenuse and the legs is true for all right triangles .
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Over 2,500 years ago, a Greek mathematician named Pythagoras developed a proof that the relationship between the hypotenuse and the legs is true for all right triangles.
In any right triangle, the square of the length of the hypotenuse is equal to the sum of the squares of the lengths of the legs."
This relationship can be stated as:
and is known as the Pythagorean Theorem
a, b are legs.c is the hypotenuse (across from the right angle).
There are certain sets of numbers that have a very special property. Not only do these numbers satisfy the Pythagorean Theorem, but any multiples of these numbers also satisfy the Pythagorean Theorem
For example: the numbers 3, 4, and 5 satisfy the Pythagorean Theorem. If you multiply all three numbers by 2 (6, 8, and 10), these new numbers ALSO satisfy the Pythagorean theorem.
If we think about a right triangle we know of course that one of the angles is a right angle. We also know that the other two angles are acute angles (why?). In fact we know that the other two angles are complementary angles. Therefore there is a relationship between the sizes of the angles that the two acute angles have measures that add up to ninety degrees.
What about sides? Is there a relationship between the sides of a right triangle? We know from previous lessons that if we have the lengths of just two of the sides we can construct the triangle so it is enough to know the lengths of two sides to determine the length of the third side. We shall now try to figure out the relationship. We shall, to make it easy to communicate assume that the length of the hypotenuse is c units and that the two legs are of length a and b units.
So according to the Pythagorean Theorem, the area of square A, plus the area of square B should equal the area of square C.
The special sets of numbers that possess this property are called
The most common Pythagorean Triples are:
3, 4, 5
5, 12, 13
8, 15, 17
Pythagorean Theorem Given:- ABC is a right angle Triangle. angle B =900R.T.P:- AC2 = AB2 +BC2Construction:- To draw BD AC .
Proof:- In Triangles ADB and ABC
AngleA=Angle A (common)
Angle ADB=Angle ABC (each 900 )
ADB ~ ABC ( A.A corollary )
So that AD/AB=AB/AC (In similar triangles corresponding sides are proportional )
AB2 = AD X AC _________(1)
Similarly BC2 = DCXAC _________(2)
Adding (1)&(2) we get
AB2 +BC2 = AD X AC + DCXAC
= AC (AD +DC)
= AC . AC
There fore AB2 +BC2 =AC2
Example 1. Find the length of AC.
AC2 = 122 + 162 (Pythagoras’ Theorem)
AC2 = 144 + 256
AC2 = 400
AC = 20
Example 2. Find the length of diagonal d .
1.A car travels 16 km from east to west. Then it turns left and travels a further 12 km.Find the displacement between the starting point and the destination point of the car.
In the figure,
AB = 16
BC = 12
AC2 = AB2 + BC2 (Pythagoras’ Theorem)
AC2 = 162 + 122
AC2 = 400
AC = 20
The displacement between the starting point and the destination point of the car is 20 km
2. The height of a tree is 5 m. The distance between
the top of it and the tip of its shadow is 13 m.
Find the length of the shadow L.
132 = 52 + L2 (Pythagoras’ Theorem)
L2 = 132 - 52
L2 = 144
L = 12
. 1.Find the length of the hypotenuse for right triangles with legs, and sketch the trianglesa).3 and 4?b).5 and 12?
c).5.2 and 10.5?
2.Find the lengths of the other leg of right triangles if one leg =6 and the hypotenuse =2,8.3 and 7 in each case.
3. A right triangle with legs equal to 5cm and 12cm. What is the length of the hypotenuse? .
4. In your own words, explain what the Pythagorean Theorem states.
Text book of class XSubject:MathematicsSearch engine:www.google.com
Prepared by S.Jaya Prada