Since these are conjugates (a conjugate is when we have anything a - anything b multiplied by anything a + anything b for the most part - this excludes things such as infinity) Since sin(x) and 1 both fit under 'anything', we have a special way of multiplying these - it's a^2-b^2, or
1^2-sin^2x=1-sin^2x=cos^2x using trigonometric properties