<p>pg. 794</p>
<p>If y is directly proportional to x^2 and y=1/8 when x=1/2 , what is the positive value of x when y = 9/2 ?</p>
<p>A 3/4
B 3/2
C 9/4
D 3
E 9</p>
<p>Need some help with this one</p>
<p>Direct proportionality:</p>
<p>a = kb
(y) = k(x^2)</p>
<p>Notice that since k is a constant, as one variable goes up, the other one must go up as well. As one goes down, the other must go down as well. That is the concept of direct proportionality.</p>
<p>y = kx^2
1/8 = k(1/2)^2
1/8 = k/4
4/8=k=1/2</p>
<p>y = (1/2)(x^2)
9/2 = (1/2)(x^2)
9=x^2
x = 3 <— ANSWER (D)</p>