SAT Math : SAT Mathematics

Study concepts, example questions & explanations for SAT Math

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Example Questions

Example Question #2 : Acute / Obtuse Isosceles Triangles

The base angle of an isosceles triangle is 27^{\circ}\(\displaystyle 27^{\circ}\).  What is the vertex angle?

Possible Answers:

75^{\circ}\(\displaystyle 75^{\circ}\)

126^{\circ}\(\displaystyle 126^{\circ}\)

149^{\circ}\(\displaystyle 149^{\circ}\)

108^{\circ}\(\displaystyle 108^{\circ}\)

135^{\circ}\(\displaystyle 135^{\circ}\)

Correct answer:

126^{\circ}\(\displaystyle 126^{\circ}\)

Explanation:

Every triangle has 180 degrees.  An isosceles triangle has one vertex angle and two congruent base angles. 

Solve the equation 27+27+x=180\(\displaystyle 27+27+x=180\) for x to find the measure of the vertex angle. 

x = 180 - 27 - 27

x = 126

Therefore the measure of the vertex angle is 126^{\circ}\(\displaystyle 126^{\circ}\).

Example Question #11 : Acute / Obtuse Isosceles Triangles

An isosceles triangle has an area of 12. If the ratio of the base to the height is 3:2, what is the length of the two equal sides?

 

Possible Answers:

4√3

4

6

5

3√3

Correct answer:

5

Explanation:

Area of a triangle is ½ x base x height. Since base:height = 3:2, base = 1.5 height.  Area = 12 = ½ x 1.5 height x height or 24/1.5 = height2.  Height = 4.  Base = 1.5 height = 6. Half the base and the height form the legs of a right triangle, with an equal leg of the isosceles triangle as the hypotenuse. This is a 3-4-5 right triangle.

 Sat_math_167_01

 

 

 

 

Example Question #171 : Geometry

Two sides of a triangle each have length 6. All of the following could be the length of the third side EXCEPT

Possible Answers:
11
12
2
3
1
Correct answer: 12
Explanation:

This question is about the Triangle Inequality, which states that in a triangle with two sides A and B, the third side must be greater than the absolute value of the difference between A and B and smaller than the sum of A and B.

Applying the Triangle Inequality to this problem, we see that the third side must be greater than the absolute value of the difference between the other two sides, which is |6-6|=0, and smaller than the sum of the two other sides, which is 6+6=12. The only answer choice that does not satisfy this range of possible values is 12 since the third side must be LESS than 12.

 

Example Question #141 : Triangles

A triangle has the following side lengths:

\(\displaystyle 13,\ 13, \textup{ and } 18\)

Which of the following correctly describes the triangle? 

Possible Answers:

Obtuse and isosceles

Obtuse and scalene

Acute and isosceles

None of these

Acute and scalene

Correct answer:

Acute and isosceles

Explanation:

The triangle has two sides of equal length, 13, so it is by definition isosceles. 

To determine whether the triangle is acute, right, or obtuse, compare the sum of the squares of the lengths of the two shortest sides to the square of the length of the longest side. The former quantity is equal to

\(\displaystyle 13^{2} + 13^{2} = 169 + 169 = 338\)

The latter quantity is equal to

\(\displaystyle 18^{2} = 324\)

The former is greater than the latter; consequently, the triangle is acute. The correct response is that the triangle is acute and isosceles.

Example Question #1 : How To Find The Area Of A Trapezoid

A trapezoid has a base of length 4, another base of length s, and a height of length s. A square has sides of length s. What is the value of s such that the area of the trapezoid and the area of the square are equal?

Possible Answers:

\(\displaystyle 4\)

\(\displaystyle 2\)

\(\displaystyle \sqrt{2}\)

\(\displaystyle 1\)

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

Correct answer:

\(\displaystyle 4\)

Explanation:

In general, the formula for the area of a trapezoid is (1/2)(a + b)(h), where a and b are the lengths of the bases, and h is the length of the height. Thus, we can write the area for the trapezoid given in the problem as follows:

area of trapezoid = (1/2)(4 + s)(s)

Similarly, the area of a square with sides of length a is given by a2. Thus, the area of the square given in the problem is s2.

We now can set the area of the trapezoid equal to the area of the square and solve for s.

(1/2)(4 + s)(s) = s2

Multiply both sides by 2 to eliminate the 1/2.

(4 + s)(s) = 2s2

Distribute the s on the left.

4s + s2 = 2s2

Subtract s2 from both sides.

4s = s2

Because s must be a positive number, we can divide both sides by s.

4 = s

This means the value of s must be 4.

The answer is 4.

Example Question #2 : How To Find The Area Of A Trapezoid

Find the area of a trapezoid given bases of length 1 and 2 and height of 2.

Possible Answers:

\(\displaystyle 4\)

\(\displaystyle 3\)

\(\displaystyle 5\)

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

Correct answer:

\(\displaystyle 3\)

Explanation:

To solve, simply use the formula for the area of a trapezoid. Thus,

\(\displaystyle A=\frac{1}{2}(b1+b2)h=\frac{1}{2}(1+2)(2)=3\)

 

Example Question #2 : How To Find The Area Of A Trapezoid

Square 1

The above figure shows Square \(\displaystyle ABCD\)\(\displaystyle M\)is the midpoint of \(\displaystyle \overline{AB}\)\(\displaystyle N\) is the midpoint of \(\displaystyle \overline{CD}\)\(\displaystyle O\) is the midpoint of \(\displaystyle \overline{CN}\). Construct \(\displaystyle \overline{MO}\)

If Square \(\displaystyle ABCD\) has area \(\displaystyle X\), what is the area of Quadrilateral \(\displaystyle AMOD\)?

Possible Answers:
\(\displaystyle \frac{5}{8} X\)

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

\(\displaystyle \frac{\sqrt{17}}{2} X\)

\(\displaystyle \frac{1}{2} X\)

\(\displaystyle \frac{\sqrt{17}}{4} X\)

Correct answer:
\(\displaystyle \frac{5}{8} X\)
Explanation:

Let \(\displaystyle t\) be the common sidelength of the square. The area of the square is \(\displaystyle X = t^{2}\).

Construct segment \(\displaystyle \overline{MN}\). This divides the square into Rectangle \(\displaystyle AMND\) and a right triangle. The dimensions of Rectangle \(\displaystyle AMND\) are 

\(\displaystyle AD = t\)

and

\(\displaystyle ND = \frac{1}{2} CD = \frac{1}{2} t\).

 

The area of Rectangle \(\displaystyle AMND\) s the product of these dimensions:

\(\displaystyle A_{1} = AD \cdot ND = t \cdot \frac{1}{2} t = \frac{1}{2} t ^{2}\)

The lengths of the legs of Right \(\displaystyle \bigtriangleup MNO\) are

\(\displaystyle MN = AD = t\)

and 

\(\displaystyle NO = \frac{1}{2} CN = \frac{1}{2} \cdot \frac{1}{2} CD = \frac{1}{2} \cdot \frac{1}{2} t = \frac{1}{4} t\)

The area of this right triangle is half the product of these lengths, or

\(\displaystyle A_{2} = \frac{1}{2} \cdot MN \cdot NO = \frac{1}{2} \cdot t \cdot \frac{1}{4} t = \frac{1}{8} t ^{2}\)

This is seen below:

Square 2

The sum of these areas is the area of Quadrilateral \(\displaystyle AMOD\)

\(\displaystyle A = A_{1}+ A_{2}= t^{2}+\frac{1}{8}t ^{2} = \frac{5}{8} t ^{2}\).

Substituting \(\displaystyle X\) for \(\displaystyle t^{2}\), the area is \(\displaystyle \frac{5}{8} X\).

Example Question #174 : Geometry

Square 1

The above figure shows Square \(\displaystyle ABCD\)\(\displaystyle M\)is the midpoint of \(\displaystyle \overline{AB}\)\(\displaystyle N\) is the midpoint of \(\displaystyle \overline{CD}\)\(\displaystyle O\) is the midpoint of \(\displaystyle \overline{CN}\). Construct \(\displaystyle \overline{MO}\)

\(\displaystyle AM = t\). Which of the following expresses the length of  \(\displaystyle \overline{MO}\) in terms of \(\displaystyle t\)?

Possible Answers:

\(\displaystyle \frac{\sqrt{5}}{2} t\)

\(\displaystyle \frac{\sqrt{17}}{4} t\)

\(\displaystyle \frac{\sqrt{65}}{8} t\)

\(\displaystyle \frac{\sqrt{63}}{8} t\)

\(\displaystyle \frac{\sqrt{15}}{4} t\)

Correct answer:

\(\displaystyle \frac{\sqrt{17}}{4} t\)

Explanation:

Construct \(\displaystyle \overline{MN}\) as shown in the diagram below:

Square 1

Quadrilateral \(\displaystyle AMND\) is a rectangle, so opposite sides are congruent. Therefore, \(\displaystyle MN = AD = t\).

Since \(\displaystyle N\) is the midpoint of \(\displaystyle \overline{CD}\),

\(\displaystyle CN = \frac{1}{2} CD = \frac{1}{2} t\)

Since \(\displaystyle O\) is the midpoint of \(\displaystyle \overline{CN}\)

\(\displaystyle ON = \frac{1}{2} CN = \frac{1}{2} \cdot \frac{1}{2} t = \frac{1}{4} t\).

\(\displaystyle \bigtriangleup MNO\) is a right triangle, so, by the Pythagorean Theorem, 

\(\displaystyle MO = \sqrt{(MN)^{2}+(NO)^{2} }\)

Substituting: 

\(\displaystyle MO= \sqrt{t^{2}+\left (\frac{1}{4}t \right)^{2} }\)

\(\displaystyle MO= \sqrt{t^{2}+ \frac {1}{16} t ^{2} }\)

\(\displaystyle MO= \sqrt{ \frac {17}{16} t ^{2} }\)

Apply the Product of Radicals and Quotient of Radicals Rules:

\(\displaystyle MO= \sqrt{ \frac {17}{16} t ^{2} }\)

\(\displaystyle = \sqrt{ \frac {17}{16} } \cdot \sqrt{t^{2}}\)

\(\displaystyle = \sqrt{ \frac {17}{16} } t\)

\(\displaystyle = \frac { \sqrt{17}}{ \sqrt{16}} \cdot t\)

\(\displaystyle = \frac { \sqrt{17}}{4} t\)

 

Example Question #1 : Parallelograms

ABCD is a parallelogram. BD = 5. The angles of triangle ABD are all equal. What is the perimeter of the parallelogram?

Figure_1

Possible Answers:

\(\displaystyle 20\)

\(\displaystyle 15\sqrt{3}\)

\(\displaystyle 10\sqrt{3}\)

\(\displaystyle 11\sqrt{2}\)

\(\displaystyle 15\)

Correct answer:

\(\displaystyle 20\)

Explanation:

If all of the angles in triangle ABD are equal and line BD divides the parallelogram, then all angles in triangle BDC must be equal as well.

We now have two equilateral triangles, so all sides of the triangles will be equal.

All sides therefore equal 5.

5+5+5+5 = 20

Example Question #171 : Plane Geometry

Find the area of a parallelogram with length 6 and height 5.

Possible Answers:

\(\displaystyle 15\)

\(\displaystyle 11\)

\(\displaystyle 22\)

\(\displaystyle 30\)

Correct answer:

\(\displaystyle 30\)

Explanation:

To solve, simply use the formula for the area of a parallelogram. Thus,

\(\displaystyle A=lh=5*6=30\)

Don't let a parallelogram fool you. It is just like a rectangle but on a slant. As long as you are given the height, and not the slant side length, you can use the same formula.

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