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Without Using Trigonometric Tables, Prove That: Sec70° Sin20° + Cos20° Cosec70° = 2 - Mathematics

Sum

Without using trigonometric tables, prove that:

sec70° sin20° + cos20° cosec70° = 2

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Solution

LHS = sec 70° sin 70° + cos 20° cosec 70°

= sec (90° - 20°) sin 20° + cos 20° cosec (90° - 20°) 

`= "cosec" 20°. 1/("cosec" 20°)+ 1/(sec 20°)  sec 20°`

= 1 + 1

= 2 

= RHS 

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APPEARS IN

RS Aggarwal Secondary School Class 10 Maths
Chapter 7 Trigonometric Ratios of Complementary Angles
Exercise | Q 3.3 | Page 313
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