Question

If cosA = 3/5 , find the value of (9 cot²A — 1).
(a) 1 (b) 16/65 (c) 65/16 (d) 0

Answer 1

ans is b)65/16

in right angle triangle ABC angle B is 90 degree

therefore AB^2 + BC^2 =AC^2

3^2+BC^2=5^2

9+BC^2=25

BC^2=25 - 9=16

BC=4

=9×(3/4)^2- 1

=9×9/16 - 1

=81/16 - 1

=81 -16/16

=65/16