ISEE Upper Level Math : Lines

Study concepts, example questions & explanations for ISEE Upper Level Math

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Example Questions

Example Question #1 : Lines

Find the distance between \displaystyle (1,4 ) and \displaystyle (-2,3).

Possible Answers:

\displaystyle \sqrt{10}

\displaystyle \sqrt{5}

\displaystyle 3

\displaystyle 10

\displaystyle \sqrt{2}

Correct answer:

\displaystyle \sqrt{10}

Explanation:

To find the distance, first remember the distance formula: \displaystyle \sqrt{(x_{2}-x_{1})^2+(y_{2}-y_{1})^2}. Plug in so that you have: \displaystyle \sqrt{(1+2)^2+(4-3)^2}. Simplify so that you get \displaystyle \sqrt{3^2+1^2}. This yields \displaystyle \sqrt{10}.

Example Question #1 : How To Find An Angle

Lines

Examine the above diagram. If \displaystyle l \parallel m, give \displaystyle y in terms of \displaystyle x.

Possible Answers:

\displaystyle 165-x

\displaystyle 131 -x

\displaystyle 165 +x

\displaystyle 75 + x

\displaystyle 75-x

Correct answer:

\displaystyle 165-x

Explanation:

The two marked angles are same-side exterior angles of parallel lines, which are supplementary - that is, their measures have sum 180. We can solve for \displaystyle y in this equation:

\displaystyle (y-17) + (x + 32) = 180

\displaystyle y + x-17 + 32= 180

\displaystyle y + x+15= 180

\displaystyle y + x+15- 15 - x = 180- 15 - x

\displaystyle y = 165- x

Example Question #31 : Geometry

Lines

Examine the above diagram. If \displaystyle l \parallel m, give \displaystyle y in terms of \displaystyle x.

Possible Answers:

\displaystyle 47 - \frac{1}{2}x

\displaystyle 184 - \frac{1}{2}x

\displaystyle 92 - \frac{1}{2}x

\displaystyle 92 - x

\displaystyle 47 - x

Correct answer:

\displaystyle 92 - \frac{1}{2}x

Explanation:

The two marked angles are same-side interior angles of parallel lines, which are supplementary - that is, their measures have sum 180. We can solve for \displaystyle y in this equation:

\displaystyle (2y + 15) + (x - 19) = 180

\displaystyle 2y + x+ 15 - 19 = 180

\displaystyle 2y + x-4 = 180

\displaystyle 2y + x-4+4 -x = 180+4 -x

\displaystyle 2y = 184 -x

\displaystyle 2y \div 2 = \left ( 184 -x \right )\div 2

\displaystyle y= 92 - \frac{1}{2}x

Example Question #31 : Isee Upper Level (Grades 9 12) Mathematics Achievement

Lines

Examine the above diagram. What is \displaystyle x + y ?

Possible Answers:

\displaystyle 82

\displaystyle 88

\displaystyle 58

\displaystyle 112

\displaystyle 68

Correct answer:

\displaystyle 68

Explanation:

By angle addition, 

\displaystyle \left ( x - 13\right )+ 100 + (y + 25) = 180

\displaystyle x - 13\right+ 100 + y + 25 = 180

\displaystyle x + y - 13\right+ 100+ 25 = 180

\displaystyle x + y +112 = 180

\displaystyle x + y +112 - 112= 180- 112

\displaystyle x + y = 68

Example Question #1 : How To Find An Angle

Lines

Examine the above diagram. Which of the following statements must be true whether or not \displaystyle l and \displaystyle m are parallel?

Possible Answers:

\displaystyle \angle 5 \cong \angle 8

\displaystyle m \angle 1 + m \angle 6 = 180 ^{\circ }

\displaystyle m \angle 4 + m \angle 7 = 180 ^{\circ }

\displaystyle \angle 2 \cong \angle 6 

\displaystyle \angle 5 \cong \angle 4

Correct answer:

\displaystyle \angle 5 \cong \angle 8

Explanation:

Four statements can be eliminated by the various parallel theorems and postulates. Congruence of alternate interior angles or corresponding angles forces the lines to be parallel, so

 \displaystyle \angle 5 \cong \angle 4 \Rightarrow l \parallel m  and

\displaystyle \angle 2 \cong \angle 6 \Rightarrow l \parallel m .

Also, if same-side interior angles or same-side exterior angles are supplementary, the lines are parallel, so 

\displaystyle m \angle 4 + m \angle 7 = 180 ^{\circ } \Rightarrow l \parallel m and 

\displaystyle m \angle 1 + m \angle 6 = 180 ^{\circ } \Rightarrow l \parallel m.

However, \displaystyle \angle 5 \cong \angle 8 whether or not \displaystyle l \parallel m since they are vertical angles, which are always congruent.

Example Question #251 : Geometry

\displaystyle \angle 1 and \displaystyle \angle 2 are supplementary; \displaystyle \angle 1 and \displaystyle \angle 3 are complementary.

\displaystyle m \angle 2 = 100 ^{\circ }.

What is \displaystyle m \angle 3 ?

Possible Answers:

\displaystyle 100^{\circ }

\displaystyle 50^{\circ }

\displaystyle 80^{\circ }

\displaystyle 10^{\circ }

Correct answer:

\displaystyle 10^{\circ }

Explanation:

Supplementary angles and complementary angles have measures totaling \displaystyle 180^{\circ } and \displaystyle 90^{\circ }, respectively.

\displaystyle m \angle 2 = 100 ^{\circ }, so its supplement \displaystyle \angle 1 has measure 

\displaystyle m \angle 1 = 180^{\circ } - m \angle 2 = 180^{\circ } - 100 ^{\circ } = 80^{\circ }

\displaystyle \angle 3, the complement of \displaystyle \angle 1, has measure 

\displaystyle m \angle 3 = 90^{\circ } - m \angle 1 = 90^{\circ } - 80 ^{\circ } = 10^{\circ }

Example Question #2 : How To Find An Angle

Thingy

Note: Figure NOT drawn to scale.

In the above figure, \displaystyle m \angle 1=\left ( x+17 \right )^{\circ} and \displaystyle m \angle 2= \left (7x+11 \right )^{\circ}. Which of the following is equal to \displaystyle m \angle 1 ?

Possible Answers:

\displaystyle 26^{\circ}

\displaystyle 36^{\circ}

\displaystyle 7\frac{3}{4}^{\circ }

\displaystyle 29\frac{5}{7}^{\circ}

\displaystyle 21\frac{5}{7}^{\circ}

Correct answer:

\displaystyle 36^{\circ}

Explanation:

\displaystyle \angle 1 and \displaystyle \angle 2 form a linear pair, so their angle measures total \displaystyle 180^{\circ}. Set up and solve the following equation:

\displaystyle m \angle 1+ m \angle 2 = 180^{\circ}

\displaystyle \left ( x+17 \right ) + \left (7x+11 \right ) = 180

\displaystyle 8x+28 = 180

\displaystyle 8x=152

\displaystyle x = 19

\displaystyle m \angle 1=\left ( x+17 \right )^{\circ} = \left ( 19+17 \right )^{\circ} = 36^{\circ}

Example Question #261 : Geometry

Two angles which form a linear pair have measures \displaystyle (2x+72)^{\circ} and \displaystyle (5x-125)^{\circ}. Which is the lesser of the measures (or the common measure) of the two angles?

Possible Answers:

\displaystyle 33\frac{2}{7}^{\circ }

\displaystyle 41\frac{3}{7}^{\circ}

\displaystyle 22\frac{6}{7}^{\circ}

\displaystyle 65\frac{2}{3 } ^{\circ }

\displaystyle 81\frac{1}{2} ^{\circ }

Correct answer:

\displaystyle 41\frac{3}{7}^{\circ}

Explanation:

Two angles that form a linear pair are supplementary - that is, they have measures that total \displaystyle 180^{\circ}. Therefore, we set and solve for \displaystyle x in this equation:

\displaystyle (2x+72)+(5x-125)= 180

\displaystyle 7x - 53 = 180

\displaystyle 7x = 233

\displaystyle x = \frac{233}{7}= 33 \frac{2}{7}

The two angles have measure

\displaystyle 2 \cdot 33 \frac{2}{7} +72= 138 \frac{4}{7} ^{\circ}

and 

\displaystyle 5 \cdot 33 \frac{2}{7} -125 = 41\frac{3}{7}^{\circ}

\displaystyle 41\frac{3}{7}^{\circ} is the lesser of the two measures and is the correct choice.

Example Question #2041 : Hspt Mathematics

Two vertical angles have measures \displaystyle (3x+14)^{\circ } and \displaystyle \left ( 5x-17\right )^{\circ }. Which is the lesser of the measures (or the common measure) of the two angles?

Possible Answers:

\displaystyle 15\frac{1}{2}^{\circ }

\displaystyle 60\frac{1}{2} ^{\circ }

\displaystyle 68\frac{5}{8}^{\circ}

\displaystyle 22\frac{7}{8}^{\circ}

\displaystyle 41\frac{1}{8}^{\circ}

Correct answer:

\displaystyle 60\frac{1}{2} ^{\circ }

Explanation:

Two vertical angles - angles which share a vertex and whose union is a pair of lines - have the same measure. Therefore, we set up and solve the equation

\displaystyle 3x+14= 5x-17

\displaystyle 14= 2x-17

\displaystyle 2x= 31

\displaystyle x= 15\frac{1}{2}

\displaystyle 3x+14 = 3 \cdot 15\frac{1}{2} + 14 = 46\frac{1}{2} + 14= 60\frac{1}{2} ^{\circ }

Example Question #1 : Lines

A line \displaystyle t intersects parallel lines \displaystyle m and \displaystyle n\displaystyle \angle 1 and \displaystyle \angle 2 are corresponding angles; \displaystyle \angle 1 and \displaystyle \angle 3 are same side interior angles.

\displaystyle m \angle 1 = \left (3x+2y \right )^{\circ }

\displaystyle m \angle 2 = \left ( 4x+21\right )^{\circ }

\displaystyle m \angle 3 = \left ( 2y-27\right )^{\circ}

Evaluate \displaystyle x+y.

Possible Answers:

\displaystyle x+y = 60

\displaystyle x+y = 45

\displaystyle x+y = 30

\displaystyle x+y = 90

\displaystyle x+y = 120

Correct answer:

\displaystyle x+y = 60

Explanation:

When a transversal such as \displaystyle t crosses two parallel lines, two corresponding angles - angles in the same relative position to their respective lines - are congruent. Therefore, 

\displaystyle 3x+2y = 4x+21

\displaystyle 3x+2y- 3x - 21 = 4x+21 - 3x - 21

\displaystyle x = 2y - 21

Two same-side interior angles are supplementary - that is, their angle measures total 180 - so

\displaystyle 3x+2y + 2y-27 = 180

\displaystyle 3x+4y-27 = 180

\displaystyle 3x+4y= 207

We can solve this system by the substitution method as follows:

\displaystyle 3( 2y - 21)+4y= 207

\displaystyle 6y-63+4y= 207

\displaystyle 10y-63= 207

\displaystyle 10y = 270

\displaystyle y = 27

Backsolve:

\displaystyle x = 2y - 21

\displaystyle x = 2 (27)- 21 = 54-21 = 33

\displaystyle x+y = 27+33 = 60, which is the correct response.

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