Cos(A-B) = cosAcosB + sinAsinB
<span>
cos(</span>π/2 - θ) = cos(π/2)cosθ + sin(π/2)sinθ
π/2 = 90°
cos(π/2) = cos90° = 0. sin(π/2) = sin90° = 1
cos(π/2 - θ) = cos(π/2)cosθ + sin(π/2)sin<span>θ
</span>
= 0*cosθ + 1*sin<span>θ = </span>sin<span>θ
Therefore </span>cos(π/2 - θ) = sin<span>θ
QED </span>
The correct answer is B. Most patients who have a poor dental experience also have post-extraction complications. This can be shown through the fact that of everyone who had a poor dental experience, 94% said they had post-extraction complication. 94% is obviously <em>most</em>. We can not confidently say that poor dental experiences cause post-extraction problems because we do not know how many people who had a normal or good experience also had problems.
