Question

if cosA =3/5, find 9 cotsquare A-1.

Answer 1

cos²A = 9/25
sin²A = 1-cos²A = 16/25

cot²A = cos²A/ sin²A = 9/16

9cot²A -1 = 81/16-1 = 65/16

Answer 2

Hey !!
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cos A = 3 / 5

We know that ,

sin2A + cos2A = 1

sin2A + (3/5 )2 = 1

sin2A = 1 - 9 /25

sin2A = 16/25

sinA = 4/5


Now !!!


cot A = cos A / sin A

= 3 / 5 × 5 / 4

= 3 / 4

Now !!


9 cot2A - 1

9 × 9 / 16 - 1

81 / 16 - 1

65/16