<p>In the xy-cordinate plane, lines l and q are perpendicular. If line l contains the points (0,0) and (2,1), and line q contains the points (2,1) and (0,t), what is the value of t?
a. -3
b. -2
c. 2
d. 3
e. 5</p>
<p>Answer is E. How to solve this without drawing anything? Is there any formula to do so?</p>
<p>Thanks</p>
<p>To find the slope of line q, which is perpendicular to line l, you must take the opposite reciprocal of the slope of line l.</p>
<p>Find the slope, which is 1/2; use the formula (y2-y1) / (x2-x1). Then take the opposite reciprocal; thus the slope of line q is -2. Then plug in to the equation and solve for y2. The value of y2 must be 5 because that is the only value for which the equation given above equals -2 (which is the necessary slope).</p>
<p>Hope this helps.</p>