Question

do with process please ​

Answer 1

Answer:

Step-by-step explanation:

From the properties of trigonometric ratios : From the properties of trigonometric ratios :

sin^2 A + cos^2 A = 1

Here, we are said to find the value of :

= > sin² ( π / 18 ) + sin² ( π / 9 ) + sin² ( 7π / 18 ) + sin² ( 4π / 9 ) + cos² ( π / 18 ) + cos² ( 7π / 18 ) + cos² ( 4π / 9 )

Grouping the terms with same angle / radian :

= > sin² ( π / 18 ) + cos² ( π / 18 ) + sin² ( 7π / 18 ) + cos² ( 7π / 18 ) + sin² ( 4π / 9 ) + cos² ( 4π / 9 ) + sin² ( π / 9 )

Using the property given above :

= > 1 + 1 + 1 + sin² ( π / 9 )

= > 3 + sin² ( π / 9 )

Using small angle approximation : sin²(π/9) ≈ ( 22 / 7 x 1 / 9 )^2

= > 3 + 0.12

≈ 3.12