text: prove that? 7/12=1/2,and cos a+sin a=1 both of you equations are not true and cannot be proved.  by '7/12' i hope you mean 7 upon 12.  7/12 = 0.5833 (recurring) 1/2  = 0.5  i reconsidered this.  'cos a + sin a' is not always equal to 1.  it may be applicable to 0°, 45° & 90° but it cannot be considered as a general formula.  sin 30° = 0.5 cos 30° = 0.866 sin 30° + cos 30° = 1.36        sin 30° + cos 30° ≠ 1 also,      sin 60° + cos 60° ≠ 1 another identity is:  sin^2 a + cos^2 a = 1 ( sin a the whole square + cos a the whole square ) = 1