# Interactive video lesson plan for: Understanding Complementary Angles in Trigonometry | Solving Problems on Complementary Angles

#### Activity overview:

Understanding Complementary Angles in Trigonometry | Solving Problems on Complementary Angles

http://www.learncbse.in/ncert-class-10-math-solutions/
http://www.learncbse.in/ncert-solutions-for-class-10-maths-chapter-8-introduction-to-trigonometry/
http://www.learncbse.in/rd-sharma-class-10-solutions-chapter-5-trigonometric-ratios/

In this video we evaluate a trigonometric expression by using trigonometric ratios of complementary angles. This is really simple. In such problems we have to make same numerator & denominator by using the trigonometric ratios of complementary angles relationship.
solve problems based on trigonometric ratios of complementary angles
Trigonometry - The Complementary Angle Theorem
use some trigonometric ratios of complementary angle

00:02 1. Solving Problems using trigonometric ratios of complementary angles
00:18 (i) sin 18° / cos 72° || 01:42 (ii) tan 26° / cot 64° || 03:07 (iii) cos 48° – sin 42° || 04:25 (iv) cosec 31° – sec 59°
00:36 COMPLEMENTARY ANGLES DEFINATION
Two angles are said to be complementary if their sum equals 90° pair of complementary angles A and (90° – A).
make same numerator & denominator by using the trigonometric ratios of complementary angles relationship.
sin (90°– A) = cos A, cos (90°– A) = sin A
05:42 Find Angle using Trigonometric Ratios of Complementary Angles q2. Show that :
06:11 Prove the trigonometric equation (i) tan 48° tan 23° tan 42° tan 67° = 1
06:28 consider LHS of trigonometric equation.
07:28 complementary angles are defined pair of two angles whose as sum equals 90°.
08:05 Important property
If A and B are complementary angles then Tan A * Tan B = 1.
09:51 (ii) cos 38° cos 52° – sin 38° sin 52° = 0
10:51 Trigonometric Ratios of Complementary Angle - Solving Problems
sin (90° – A) = cos A, cos (90° – A) = sin A ,
12:16 Find Angle using Trigonometric Ratios of Complementary Angles q3. If tan 2A = cot (A – 18°), where 2A is an acute angle, find the value of A.
12:20 Trigonometric Ratios of Complementary Angle- Find the Angle Problems
12:59 use rigonometric ratios of complementary angle
tan (90° – A) = cot A, cot (90° – A) = tan A,
14:42 Find Angle using Trigonometric Ratios of Complementary Angles q4. If tan A = cot B, prove that A + B = 90°.
15:24 trigonometric ratios of complementary angle
cot (90° – A) = tan A, tan (90° – A) = cot A,
16:07 Find Angle using Trigonometric Ratios of Complementary Angles q5. If sec 4A = cosec (A – 20°), where 4A is an acute angle, find the value of A.
17:00 trigonometric ratios of complementary angle, sec (90° – A) = cosec A, cosec (90° – A) = sec A,
18:54 Trigonometric Ratios of Complementary Angle- Find the Angle Problems q6. If A, B and C are interior angles of a triangle ABC, then show that trigonometric equation sin( (A+B)/2 ) = cos A/2
19:24 Angle sum property of triangle : Sum of angles in a triangle is 180°.
19:58 Take LHS of trigonometric equation
21:25 Trigonometric Ratios of Complementary Angle- Find the Angle Problems q7. Express sin 67° + cos 75° in terms of trigonometric ratios of angles between 0° and 45°.
22:09 take Trigonometric Ratios of Complementary Angle
sin (90° – A) = cos A, cos (90° – A) = sin A ,

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