Q.

Assertion (A): If two acute angles add up to 90°, their sines are equal.

Reason (R): The sum of angles in a right triangle is 180°, and one of the angles is 90°.

1 Both A and R are true, and R is the correct explanation of A.  
2 Both A and R are true, but R is not the correct explanation of A.  
3 A is true, but R is false.  
4 A is false, but R is true.  

Ans.

(4)

The assertion is false because the sine of angles that add up to 90° are equal to its cosine and vice-versa. The reason is true, as it describes the fundamental property of angle sums in a right triangle.