TRIGONOMETRIC FUNCTIONS OF ACUTE ANGLES By M. Jaya krishna Reddy Mentor in mathematics, APIIIT- Basar , Adilabad ( dt ),A.P. India.

Acute Angle: :

Acute Angle : ACUTE ANGLE An angle whose measure is greater than zero but less than 90 is called an “acute angle” o Initial ray T E R M I N A L R A Y

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S ome O ld H ouses C an’t A lways H ide T heir O ld A ge Commonly used mnemonic for these ratios : Ѳ c a b B C A

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Trigonometric functions(also called circular functions) are functions of an angle. History : They are used to relate the angles of a triangle to the lengths of the sides of a triangle. Sumerian astronomers introduced angle measure, using a division of circles into 360 degrees. The sine function was first defined in the “ surya siddhanta ” and its properties were further documented by the fifth century Indian mathematician and astronomer “ Aryabhatta ”. By 10 th century the six trigonometric functions were used.

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Applications : In 240 B.C. a mathematician named “Eratosthenes” discovered the radius of the earth as 4212.48 miles using trigonometric functions.. In 2001 a group of European astronomers did an experiment by using trigonometric functions and they got all the measurement, they calculate the Venus was about 105,000,000 km away from the sun and the earth was about 150, 000, 000 km away. Optics and statics are 2 early fields of Physics that use trigonometry. It is also the foundation of the practical art of surveying

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1. Prove that 2. Prove that Sol: Sol:

Fundamental Relations::

Fundamental Relations : Squaring and adding both the equations Ѳ c a b C A B From the above diagram, By Pythagorean Rule,

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Squaring and subtracting the equations, we get Similarly, Ѳ c a b C A B From the above diagram, By Pythagorean Rule,

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Example: Prove that sol:

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Ex: Prove that sec 2 Ѳ - cosec 2 Ѳ = tan 2 Ѳ - cot 2 Ѳ Sol: We know that sec 2 Ѳ - tan 2 Ѳ = 1 = cosec 2 Ѳ - cot 2 Ѳ sec 2 Ѳ - tan 2 Ѳ = cosec 2 Ѳ - cot 2 Ѳ sec 2 Ѳ - cosec 2 Ѳ = tan 2 Ѳ - cot 2 Ѳ Example: Prove that Sol: Given that

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0 0 30 0 45 0 60 0 90 0 Sin 0 1 Cos 1 0 Tan 0 1 ∞ Cosec ∞ 2 1 Sec 1 2 ∞ Cot ∞ 1 0 Values of the trigonometrical ratios :

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Example: find the value of tan45 0 .sec30 0 - cot90 0 .cosec45 0 Sol: Given that tan45 0 .sec30 0 -- cot90 0 .cosec45 0 = 1 . -- 0. = Example: If cos Ѳ = 3/5, find the value of the other ratios Ѳ 5 4 3 Sol: Given that cos Ѳ = 3/5 = adj / hyp thus using reference triangle adj = 3, hyp = 5,by Pythagorean principle opp = 4

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