MathDB

1954 AMC 12/AHSME

Part of AMC 12/AHSME

Subcontests

(50)

Points of Tangency

In the diagram, if points A A, B B and C C are points of tangency, then x x equals: [asy]unitsize(5cm); defaultpen(linewidth(.8pt)+fontsize(8pt)); dotfactor=3;
pair A=(-3*sqrt(3)/32,9/32), B=(3*sqrt(3)/32, 9/32), C=(0,9/16); pair O=(0,3/8);
draw((-2/3,9/16)--(2/3,9/16)); draw((-2/3,1/2)--(-sqrt(3)/6,1/2)--(0,0)--(sqrt(3)/6,1/2)--(2/3,1/2)); draw(Circle(O,3/16)); draw((-2/3,0)--(2/3,0));
label("AA",A,SW); label("BB",B,SE); label("CC",C,N); label("38\frac{3}{8}",O); draw(O+.07*dir(60)--O+3/16*dir(60),EndArrow(3)); draw(O+.07*dir(240)--O+3/16*dir(240),EndArrow(3)); label("12\frac{1}{2}",(.5,.25)); draw((.5,.33)--(.5,.5),EndArrow(3)); draw((.5,.17)--(.5,0),EndArrow(3)); label("xx",midpoint((.5,.5)--(.5,9/16))); draw((.5,5/8)--(.5,9/16),EndArrow(3)); label("6060^{\circ}",(0.01,0.12)); dot(A); dot(B); dot(C);[/asy]<spanclass=latexbold>(A)</span> 316"<spanclass=latexbold>(B)</span> 18"<spanclass=latexbold>(C)</span> 132"<spanclass=latexbold>(D)</span> 332"<spanclass=latexbold>(E)</span> 116" <span class='latex-bold'>(A)</span>\ \frac {3}{16}" \qquad <span class='latex-bold'>(B)</span>\ \frac {1}{8}" \qquad <span class='latex-bold'>(C)</span>\ \frac {1}{32}" \qquad <span class='latex-bold'>(D)</span>\ \frac {3}{32}" \qquad <span class='latex-bold'>(E)</span>\ \frac {1}{16}"

A Rhombus

In a rhombus, ABCD ABCD, line segments are drawn within the rhombus, parallel to diagonal BD BD, and terminated in the sides of the rhombus. A graph is drawn showing the length of a segment as a function of its distance from vertex A A. The graph is: <spanclass=latexbold>(A)</span> A straight line passing through the origin.<spanclass=latexbold>(B)</span> A straight line cutting across the upper right quadrant.<spanclass=latexbold>(C)</span> Two line segments forming an upright V.<spanclass=latexbold>(D)</span> Two line segments forming an inverted V.<spanclass=latexbold>(E)</span> None of these. <span class='latex-bold'>(A)</span>\ \text{A straight line passing through the origin.} \\ <span class='latex-bold'>(B)</span>\ \text{A straight line cutting across the upper right quadrant.} \\ <span class='latex-bold'>(C)</span>\ \text{Two line segments forming an upright V.} \\ <span class='latex-bold'>(D)</span>\ \text{Two line segments forming an inverted V.} \\ <span class='latex-bold'>(E)</span>\ \text{None of these.}

Considering Graphs

Consider the graphs of (1): y\equal{}x^2\minus{}\frac{1}{2}x\plus{}2 and (2) y\equal{}x^2\plus{}\frac{1}{2}x\plus{}2 on the same set of axis. These parabolas are exactly the same shape. Then: <spanclass=latexbold>(A)</span> the graphs coincide.<spanclass=latexbold>(B)</span> the graph of (1) is lower than the graph of (2).<spanclass=latexbold>(C)</span> the graph of (1) is to the left of the graph of (2).<spanclass=latexbold>(D)</span> the graph of (1) is to the right of the graph of (2).<spanclass=latexbold>(E)</span> the graph of (1) is higher than the graph of (2). <span class='latex-bold'>(A)</span>\ \text{the graphs coincide.} \\ <span class='latex-bold'>(B)</span>\ \text{the graph of (1) is lower than the graph of (2).} \\ <span class='latex-bold'>(C)</span>\ \text{the graph of (1) is to the left of the graph of (2).} \\ <span class='latex-bold'>(D)</span>\ \text{the graph of (1) is to the right of the graph of (2).} \\ <span class='latex-bold'>(E)</span>\ \text{the graph of (1) is higher than the graph of (2).}

Midpoint of Line Segment

The locus of the midpoint of a line segment that is drawn from a given external point P P to a given circle with center O O and radius r r, is: <spanclass=latexbold>(A)</span> a straight line perpendicular to PO<spanclass=latexbold>(B)</span> a straight line parallel to PO<spanclass=latexbold>(C)</span> a circle with center P and radius r<spanclass=latexbold>(D)</span> a circle with center at the midpoint of PO and radius 2r<spanclass=latexbold>(E)</span> a circle with center at the midpoint PO and radius 12r <span class='latex-bold'>(A)</span>\ \text{a straight line perpendicular to }\overline{PO} \\ <span class='latex-bold'>(B)</span>\ \text{a straight line parallel to } \overline{PO} \\ <span class='latex-bold'>(C)</span>\ \text{a circle with center }P\text{ and radius }r \\ <span class='latex-bold'>(D)</span>\ \text{a circle with center at the midpoint of }\overline{PO}\text{ and radius }2r \\ <span class='latex-bold'>(E)</span>\ \text{a circle with center at the midpoint }\overline{PO}\text{ and radius }\frac{1}{2}r

Evaluating Expressions

The expression 2x2x(x+1)(x2)4+x(x+1)(x2) \frac{2x^2-x}{(x+1)(x-2)}-\frac{4+x}{(x+1)(x-2)} cannot be evaluated for x=1 x=-1 or x=2 x=2, since division by zero is not allowed. For other values of x x:
<spanclass=latexbold>(A)</span> The expression takes on many different values.<spanclass=latexbold>(B)</span> The expression has only the value 2.<spanclass=latexbold>(C)</span> The expression has only the value 1.<spanclass=latexbold>(D)</span> The expression always has a value between 1 and +2.<spanclass=latexbold>(E)</span> The expression has a value greater than 2 or less than 1.<span class='latex-bold'>(A)</span>\ \text{The expression takes on many different values.} \\ <span class='latex-bold'>(B)</span>\ \text{The expression has only the value 2.} \\ <span class='latex-bold'>(C)</span>\ \text{The expression has only the value 1.} \\ <span class='latex-bold'>(D)</span>\ \text{The expression always has a value between } -1 \text{ and } +2. \\ <span class='latex-bold'>(E)</span>\ \text{The expression has a value greater than 2 or less than } -1.