First, let's work out a problem of linear equation. This part of the linear equation in American high schools mainly includes oblique intersection, oblique intersection of points, general and determination of the position of two straight lines. The topic is as follows:

Vertical means vertical. The question is to ask which of the five options is perpendicular to the straight line given in the question. This topic is very simple. I only know that the slopes of two vertical lines are negative reciprocal, so the answer is D.

Give me another question.

θ is an acute angle. Given the value of sinθ, what is cosθ? The topic itself is very simple, and it examines the double-angle formula: cos2θ= 1-2sin? θ

So it can be calculated that the answer is a.