SAT II Math II : SAT Subject Test in Math II

Study concepts, example questions & explanations for SAT II Math II

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Example Questions

Example Question #1 : Solving Exponential, Logarithmic, And Radical Functions

Find \(\displaystyle x\):   \(\displaystyle \sqrt{-3x-5} = 7\)

Possible Answers:

\(\displaystyle -4\)

\(\displaystyle 18\)

\(\displaystyle -18\)

\(\displaystyle -9\)

\(\displaystyle -54\)

Correct answer:

\(\displaystyle -18\)

Explanation:

Square both sides to eliminate the radical.

\(\displaystyle (\sqrt{-3x-5}) ^2= 7^2\)

\(\displaystyle -3x-5 = 49\)

Add five on both sides.

\(\displaystyle -3x-5 +5= 49+5\)

\(\displaystyle -3x = 54\)

Divide by negative three on both sides.

\(\displaystyle \frac{-3x}{-3} = \frac{54}{-3}\)

The answer is:  \(\displaystyle -18\)

Example Question #2 : Solving Functions

If \(\displaystyle f(x) = 2\sqrt{x}-\sqrt{x-3}\), what is the value of \(\displaystyle f(-3)\)?

Possible Answers:

\(\displaystyle -2i\sqrt3\)

\(\displaystyle 2i\sqrt3 -i\sqrt6\) 

\(\displaystyle -12i\)

\(\displaystyle i\sqrt6\)

\(\displaystyle 0\)

Correct answer:

\(\displaystyle 2i\sqrt3 -i\sqrt6\) 

Explanation:

Substitute the value of negative three as \(\displaystyle x\).

\(\displaystyle f(-3) = 2\sqrt{-3}-\sqrt{(-3)-3}\)

\(\displaystyle 2\sqrt{-3}-\sqrt{-6} = 2\sqrt{-1}\cdot \sqrt{3} - \sqrt{-1}\cdot \sqrt{6}\)

The terms will be imaginary.  We can factor out an \(\displaystyle i = \sqrt{-1}\) out of the right side.  Replace them with \(\displaystyle i\).

The answer is:  \(\displaystyle 2i\sqrt3 -i\sqrt6\)

Example Question #61 : Functions And Graphs

A baseball is thrown straight up with an initial speed of 60 feet per second by a man standing on the roof of a 100-foot high building. The height of the baseball in feet as a function of time  \(\displaystyle t\) in seconds is modeled by the function

\(\displaystyle h(t) = -16t^{2}+60t + 100\)

To the nearest tenth of a second, how long does it take for the baseball to hit the ground?

Possible Answers:

\(\displaystyle 1.3\textrm{ sec}\)

\(\displaystyle 100\textrm{ sec}\)

\(\displaystyle 6.4\textrm{ sec}\)

\(\displaystyle 5.0 \textrm{ sec}\)

\(\displaystyle 3.8\textrm{ sec}\)

Correct answer:

\(\displaystyle 5.0 \textrm{ sec}\)

Explanation:

When the baseball hits the ground, the height is 0, so we set \(\displaystyle h\left ( t\right ) = 0\). and solve for \(\displaystyle t\).

\(\displaystyle -16t^{2}+60t + 100 = 0\)

This can be done using the quadratic formula:

\(\displaystyle t = \frac{-b \pm \sqrt{b^{2}-4ac}}{2a}\)

Set \(\displaystyle a = -16, b = 60, c = 100\):

\(\displaystyle t = \frac{-60 \pm \sqrt{60^{2}-4(-16)100}}{2(-16)}\)

\(\displaystyle t = \frac{-60 \pm \sqrt{3,600- (- 6,400)}}{-32}\)

\(\displaystyle t = \frac{-60 \pm \sqrt{3,600+6,400}}{-32}\)

\(\displaystyle t = \frac{-60 \pm \sqrt{10,000}}{-32}\)

\(\displaystyle t = \frac{-60 \pm 100}{-32}\)

One possible solution:

\(\displaystyle t = \frac{-60 + 100}{-32} = \frac{40}{-32} = -1.25\) 

We throw this out, since time must be positive.

The other:

\(\displaystyle t = \frac{-60 - 100}{-32} = \frac{-160}{-32} = 5\)

This solution, we keep. The baseball hits the ground in 5 seconds.

 

Example Question #1 : Solving Trigonometric Functions

Give the period of the graph of the equation

\(\displaystyle f(x) = \frac{2}{9} \sin 8 x\)

Possible Answers:

\(\displaystyle 8\)

The correct answer is not among the other choices.

\(\displaystyle \frac{1}{8}\)

\(\displaystyle \frac{2}{9}\)

\(\displaystyle \frac{9}{2}\)

Correct answer:

The correct answer is not among the other choices.

Explanation:

The period of the graph of a sine function \(\displaystyle f(x)= A \sin Bx\) is \(\displaystyle \frac{2 \pi}{B}\), or \(\displaystyle 2 \pi \div B\).

Since \(\displaystyle B= 8\),

\(\displaystyle 2 \pi \div 8 = \frac{\pi }{4}\).

This answer is not among the given choices.

Example Question #1 : Solving Trigonometric Functions

If \(\displaystyle f(x)=2sin(x)+cos(x)\), what must \(\displaystyle f(\frac{\pi}{4})\) be?

Possible Answers:

\(\displaystyle \frac{\sqrt2}{2}+2\)

\(\displaystyle \frac{3\sqrt2}{2}\)

\(\displaystyle 4\sqrt2\)

\(\displaystyle \textup{The answer is not given.}\)

\(\displaystyle 3\sqrt{2}\)

Correct answer:

\(\displaystyle \frac{3\sqrt2}{2}\)

Explanation:

Evaluate each trig function at the specified angle.

\(\displaystyle sin(\frac{\pi}{4}) = \frac{\sqrt{2}}{2}\)

\(\displaystyle cos(\frac{\pi}{4}) = \frac{\sqrt{2}}{2}\)

Replace the terms into the function.

\(\displaystyle f(\frac{\pi}{4})=2sin(\frac{\pi}{4})+cos(\frac{\pi}{4}) = 2(\frac{\sqrt{2}}{2})+\frac{\sqrt{2}}{2}\)

Combine like-terms.

The answer is:  \(\displaystyle \frac{3\sqrt2}{2}\)

Example Question #1 : Solving Piecewise And Recusive Functions

Define \(\displaystyle f\) and \(\displaystyle g\) as follows:

\(\displaystyle f(x) = \left\{\begin{matrix} x+ 2,& x < 0 \\ 4-x, & x \geq 0 \end{matrix}\right.\)

\(\displaystyle g(x) = \left\{\begin{matrix} 4x ,& x < 3 \\ 3x, & x \geq 3 \end{matrix}\right.\)

Evaluate \(\displaystyle (f \circ g) \left ( 3\right )\).

Possible Answers:

\(\displaystyle (f \circ g) \left ( 3\right ) = 11\)

\(\displaystyle (f \circ g) \left ( 3\right ) = -5\)

\(\displaystyle (f \circ g) \left ( 3\right ) = 3\)

\(\displaystyle (f \circ g) \left ( 3\right ) = 4\)

\(\displaystyle (f \circ g) \left ( 3\right ) = -8\)

Correct answer:

\(\displaystyle (f \circ g) \left ( 3\right ) = -5\)

Explanation:

\(\displaystyle (f \circ g) \left ( x\right ) = f (g(x))\) by definition.

 

\(\displaystyle (f \circ g) \left ( 3\right ) = f (g (3))\)

\(\displaystyle g(x) = 3x\) on the set \(\displaystyle [3, \infty)\), so 

\(\displaystyle g(3) = 3 \cdot 3 = 9\).

\(\displaystyle f(x) = 4-x\) on the set \(\displaystyle [0 , \infty)\), so

\(\displaystyle f (g(3)) = f(9) = 4-9 = -5\).

Example Question #1 : Solving Piecewise And Recusive Functions

Define function \(\displaystyle f\) as follows:

\(\displaystyle f(x) = \left\{\begin{matrix} 2x- 5 &x< 0 \\ -3x & x \ge 0 \end{matrix}\right.\)

Give the range of \(\displaystyle f\).

Possible Answers:

\(\displaystyle (-\infty, 5)\)

\(\displaystyle (-5, 0]\)

\(\displaystyle (-\infty, -5)\)

\(\displaystyle (-\infty, \infty)\)

\(\displaystyle (-\infty, 0]\)

Correct answer:

\(\displaystyle (-\infty, 0]\)

Explanation:

The range of a piecewise function is the union of the ranges of the individual pieces, so we examine both of these pieces.

If \(\displaystyle x < 0\), then \(\displaystyle f(x) = 2x - 5\). To find the range of \(\displaystyle f\) on the interval \(\displaystyle (-\infty, 0)\), we note:

\(\displaystyle x < 0\)

\(\displaystyle 2x < 2 \cdot 0\)

\(\displaystyle 2x < 0\)

\(\displaystyle 2x- 5 < 0 - 5\)

\(\displaystyle 2x- 5 < - 5\)

\(\displaystyle f(x)< - 5\)

The range of this portion of \(\displaystyle f\) is \(\displaystyle (-\infty, -5)\).

 

If \(\displaystyle x \ge 0\), then \(\displaystyle f(x) = -3x\). To find the range of \(\displaystyle f\) on the interval \(\displaystyle [0, \infty)\), we note:

\(\displaystyle x \ge 0\)

\(\displaystyle -3x \le -3 \cdot 0\)

\(\displaystyle -3x \le 0\)

\(\displaystyle f(x)\le 0\)

The range of this portion of \(\displaystyle f\) is \(\displaystyle (-\infty, 0 ]\)

 

The union of these two sets is \(\displaystyle (-\infty, 0 ]\), so this is the range of \(\displaystyle f\) over its entire domain.

Example Question #11 : Solving Functions

Define function \(\displaystyle f\) as follows:

\(\displaystyle f(x) = \left\{\begin{matrix} x- 7 &x< -1 \\ 6-x & x > 1 \end{matrix}\right.\)

Give the range of \(\displaystyle f\).

Possible Answers:

\(\displaystyle ( -8 , \infty)\)

\(\displaystyle (-\infty, \infty)\)

\(\displaystyle (-\infty, 5)\)

\(\displaystyle (-\infty, -8)\)

\(\displaystyle (-\infty, -8) \cup (5, \infty)\)

Correct answer:

\(\displaystyle (-\infty, 5)\)

Explanation:

The range of a piecewise function is the union of the ranges of the individual pieces, so we examine both of these pieces.

 

If \(\displaystyle x < -1\), then \(\displaystyle f(x)=x-7\)

To find the range of \(\displaystyle f\) on the interval \(\displaystyle (-\infty, -1)\), we note:

\(\displaystyle x < -1\)

\(\displaystyle x-7 < -1-7\)

\(\displaystyle f(x)< -8\)

The range of \(\displaystyle f\) on \(\displaystyle (-\infty, -1)\) is \(\displaystyle (-\infty, -8)\).

 

If \(\displaystyle x > 1\), then \(\displaystyle f(x)=6-x\)

To find the range of \(\displaystyle f\) on the interval \(\displaystyle (1, \infty )\), we note:

\(\displaystyle x > 1\)

\(\displaystyle -x < - 1\)

\(\displaystyle 6-x < 6- 1\)

\(\displaystyle f(x)< 5\)

The range of \(\displaystyle f\) on \(\displaystyle (1, \infty )\) is \(\displaystyle (-\infty, 5)\).

 

The range of \(\displaystyle f\) on its entire domain is the union of these sets, or \(\displaystyle (-\infty, 5)\).

Example Question #2 : Solving Piecewise And Recusive Functions

Define functions \(\displaystyle f\) and \(\displaystyle g\) as follows:

\(\displaystyle f(x)= 4x+7\)

\(\displaystyle g(x) = \left\{\begin{matrix} x+ 6 &x< 0 \\ x- 3 & x \ge 0 \end{matrix}\right.\)

Evaluate \(\displaystyle (f \circ g) \left ( 2\frac{1}{3}\right )\).

Possible Answers:

\(\displaystyle 40\frac{1}{3}\)

\(\displaystyle 4\frac{1}{3}\)

\(\displaystyle 13\frac{1}{3}\)

\(\displaystyle 22\frac{1}{3}\)

Undefined

Correct answer:

\(\displaystyle 4\frac{1}{3}\)

Explanation:

\(\displaystyle (f \circ g) \left ( 2\frac{1}{3}\right )=f\left ( g \left ( 2\frac{1}{3}\right ) \right )\)

First, we evaluate  \(\displaystyle g \left ( 2\frac{1}{3}\right )\). Since \(\displaystyle 2\frac{1}{3} \ge 0\), the definition of \(\displaystyle g\) for \(\displaystyle x \ge 0\) is used, and 

\(\displaystyle g(x)= x-3\)

\(\displaystyle g \left ( 2\frac{1}{3}\right ) = 2\frac{1}{3} - 3 = -\frac{2}{3}\)

Since 

\(\displaystyle f(x)= 4x+7\), then

\(\displaystyle (f \circ g) \left ( 2\frac{1}{3}\right )\)

\(\displaystyle =f\left ( g \left ( 2\frac{1}{3}\right ) \right )\)

\(\displaystyle =f\left ( -\frac{2}{3} \right )\)

\(\displaystyle = 4 \left ( -\frac{2}{3} \right )+7\)

\(\displaystyle = -2\frac{2}{3} +7\)

\(\displaystyle = 4\frac{1}{3}\)

Example Question #1 : Solving Piecewise And Recusive Functions

Define functions \(\displaystyle f\) and \(\displaystyle g\) as follows:

\(\displaystyle f(x) = \left\{\begin{matrix} 2x &x< -1 \\ 3x & x > 1 \end{matrix}\right.\)

\(\displaystyle g(x) = \left\{\begin{matrix} x+ 5 &x< -1 \\ x- 2 & x > 1 \end{matrix}\right.\)

Evaluate Evaluate \(\displaystyle (f \circ g)(3)\).

Possible Answers:

Undefined

\(\displaystyle 16\)

\(\displaystyle 3\)

\(\displaystyle 2\)

\(\displaystyle 24\)

Correct answer:

Undefined

Explanation:

\(\displaystyle (f \circ g)(3) = f(g(3))\)

First, evaluate \(\displaystyle g(3)\) using the definition of \(\displaystyle g\) for \(\displaystyle x > 1\):

\(\displaystyle g(x)= x-2\)

\(\displaystyle g(3)= 3-2 = 1\)

Therefore, 

\(\displaystyle (f \circ g)(3) = f(g(3)) = f(1)\)

However, \(\displaystyle x = 1\) is not in the domain of \(\displaystyle f\)

Therefore, \(\displaystyle (f \circ g)(3)\) is an undefined quantity.

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