<p>on the new sat CB blue book, i don't understand that.</p>
<p>there are a like 2 hard/tricky questions per section. the sat used to be easy, but the math is getting pretty hard.</p>
<p>This is actually a lot simpler than it looks.</p>
<p>They give you that the line, l, is perpendicular to 4x + y = k, or y = -4x + k in slope intercept form. This tells you that the slope of your line, l, is 1/4 (the negative reciprocal of the slope of the given line, which was -4). They also tell you that your line passes through the origin, so 0 is the y-intercept. Therefore, the equation of your line, l, is simply y = 1/4x. Now they want you to find the value of t, given that these two lines intersect at (t, t+1).</p>
<p>This makes it seem as if you need to someone involve both equations, but they tell you that the lines intersect at this point, so plugging it into both equations would yield the same result. Since you are not given the value of k, however, you can simply use the equation of line l to solve for the value of t by substition:</p>
<p>y = 1/4x
(t+1) = 1/4(t)
(-3/4)t = 1
t = -4/3 --> Answer choice A.</p>
<p>ok, i got that the equation of y= 1/4x...</p>
<p>i didn't understand about getting -3/4...</p>
<p>where does the -3 come from?</p>
<p>nvm... i can take a hit and not understand a few questiolns. i omitted two in that section of 20 questions. and got 18 right</p>
<p>Hey, sorry... I went away:</p>
<p>What's in brackets [], is what was substituted in. [t+1] is the y value, so I substituted for y, and [t] is the x value, so I substituted for x ( in y = (1/4)x ).</p>
<p>[t+1] = (1/4)<a href="-3/4">t</a>t = 1 (Subtract t from each side)
t = -4/3 (Divide each side by -3/4)</p>
<p>Everything Zach said was right in his first paragraph. The equation to the perpendicular line is y=1/4x. However, I don't know if anyone else found his equation confusing but here is a second explanation to consider, mine is longer but I seem to understand it. Maybe someone else might understand my way too. </p>
<p>1st Step: y=1/4x (Original Equation)<br>
2nd Step: (t+1)=1/4(t) (Plug in values; y=(t+1) and x=(t))
3rd Step: 4(t+1)=t (Multiply both sides by 4 in order to eliminate the 1/4 and isolate t.)
4th Step: 4t+4=t (Use Distribution.)
5th Step: 4=t-4t (Put like terms on the same side.)
6th Step: 4=-3t (Subtract.)
7th Step: -4/3=t (Divide and there's the answer.)</p>
<p>Once you understand the problem, working this equation will go much more quickly. Most of these steps you should be able to do in your head to save time. However, I worked the problem the long way in order to limit confusion. I hope my suggestion was at least slightly helpful.</p>
<p>so do you just disregard the k since it was a "constant"? =/</p>
<p>for this problem i first got the equation for the line that goes through the origin: y=x/4 and then set up the equation:
x/4=x+1
solve for x and get A</p>
<p>What's with the 2.5 year bump?</p>