<p>can anyone explain these questions to me?</p>
<ol>
<li>If m and n are constants, what is the value of n if the equation (x+9)(x+m)=x^2+4mx+n is true for all values of x?</li>
</ol>
<p>a) 9
b) 18
c) 27
d) 36
e) 48</p>
<ol>
<li>If x is directly proportional to radical y, then y is inversely proportional to:</li>
</ol>
<p>a) x^2
b) radical x
c) 1/radical x
d) 1/x
e) 1/x^2</p>
<p>is the answer c for question 15?</p>
<p>for #16, start by FOILing</p>
<p>(x+9)(x+m)=x^2+4mx+n
x^2+9x+mx+9m = x^2+4mx+n</p>
<p>Then do a little clever factoring on the left:</p>
<p>x^2+(9+m)x+9m = x^2+4mx+n</p>
<p>Now you know 9+m = 4m, and 9m = n</p>
<p>Solve the first one for m:</p>
<p>9=3m
3=m</p>
<p>And then you know n = 9m = 9(3) = 27</p>
<h1>15 is E.</h1>
<p>If x is directly proportional to radical y, then you can also say x^2 is proportional to y.</p>
<p>Think about proportionality for a second with different variables: If r is proportional to s, then r is INVERSELY proportional to 1/s. That is to say if (and I wish I could do sub-numbers here):
r1/s1=r2/s2, which is the definition of direct proportionality,</p>
<p>then you can also say r1(1/s1)=r2(1/s2), which is an awkward way of stating inverse proportionality. So if r is proportional to s, then r is inversely proportional to 1/s.</p>
<p>Back to our problem. If x^2 is proportional to y, then 1/x^2 is inversely proportional to y.</p>
<p>Don’t worry too much about this one if you’re taking the SAT tomorrow. Inverse proportionality is pretty unlikely to appear on your test.</p>
<p>thanks for the help PWN, I’m not taking the real SAT tomorrow but I plan to take a practice SAT.</p>