This equation is not true in general.
Starting with the left side of the equation:sin^2a + ctg^2a + cos^2a= sin^2a + (1/tan^2a) + cos^2a= sin^2a + (1/cos^2a) + cos^2a= sin^2a + sec^2a + cos^2a= 1 (by trigonometric identity)
Therefore, the given equation simplifies to 1, not 1/sin^2a.
This equation is not true in general.
Starting with the left side of the equation:
sin^2a + ctg^2a + cos^2a
= sin^2a + (1/tan^2a) + cos^2a
= sin^2a + (1/cos^2a) + cos^2a
= sin^2a + sec^2a + cos^2a
= 1 (by trigonometric identity)
Therefore, the given equation simplifies to 1, not 1/sin^2a.