Without using trigonometric tables, prove that:

sin² 28° - cos² 62° = 0

Without using trigonometric tables, prove that:

cos² 25° + cos² 65° = 1

Without using trigonometric tables, prove that:

sec² 22° - cot² 68° = 1

Without using trigonometric tables, prove that:

sin 63° cos 27° + cos 63° sin 27° = 1