<p>For the circled problem, I don't understand why the correct answer is A. I read the explanation at the back of the book, but I still don't get it. Help?</p>
<p>The numbers on the figure are 150 (inner), 6 (bottom), and 4 (side), if it isn't clear.</p>
<p>Because you are not given the altitude, but the slanted sides length. So in this case, use the following formula:</p>
<p>A = L1 * L2 * sin(angle)</p>
<p>You plug into this formula, with the angle and lengths given, and get the following:</p>
<p>A = 4<em>6</em>sin(150), and you know that sin(150) = sin(30) = (1/2)</p>
<p>So in truth it ends up being:</p>
<p>A= 4 * 6 * (1/2) = 24 * (1/2) = 12, which is the final answer.</p>
<p>In case you didn’t know that formula, you could find the altitude is two since it is part of a 30-60-90 triangle. The hypotenuse in the diagram is 4 so the altitude is 6. If you were to move one of the triangles drawn to the other side you would get a rectangle with side length 6 and height 2. Multiply to get 12.</p>
<p>Oh wow. Its just the base then the height? I found the height to be 2, but then I stopped there because I just wasn’t sure what to do next. I didn’t pick 12 because I thought it was a trap…I thought i had to do the areas of both the smaller triangles, the area of the square, then add them…but thanks…</p>
<p>Did we have to memorize all the formula? Or are they printed on the test info?</p>
<p>They have some basic formulas for geometric figures, but parallelogram should be easy to memorize; you just have to find height and base.</p>
