High School Math : Algebra I

Study concepts, example questions & explanations for High School Math

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Example Questions

Example Question #91 : Algebra I

A straight line passes through the points \(\displaystyle (1,3)\) and \(\displaystyle (2,2)\).

What is the \(\displaystyle x\)-intercept of this line?

Possible Answers:

\(\displaystyle (0,5)\)

\(\displaystyle (0,4)\)

\(\displaystyle (5,0)\)

\(\displaystyle (3,1)\)

\(\displaystyle (4,0)\)

Correct answer:

\(\displaystyle (4,0)\)

Explanation:

First calculate the slope:

\(\displaystyle (\text{change in Y})/(\text{change in x}) = (1-2)/(3-2) = -1\)

The standard equation for a line is  \(\displaystyle Y=a*X + b\).

In this equation, \(\displaystyle a\) is the slope of the line, and \(\displaystyle b\) is the \(\displaystyle y\)-intercept. All points on the line must fit this equation. Plug in either point (1,3) or (2,2).

Plugging in (1,3) we get \(\displaystyle 3=-1*1 + b\).

Therefore, \(\displaystyle b = 3 - (-1) =4\).

Our equation for the line is now:

\(\displaystyle Y= (-1)X + 4\)

To find the \(\displaystyle x\)-intercept, we plug in \(\displaystyle y=0\):

\(\displaystyle 0=(-1)x+4\) 

 \(\displaystyle x=4\)

Thus, the \(\displaystyle x\)-intercept the point (4,0).

Example Question #92 : Algebra I

Calculate the y-intercept of the line depicted by the equation below.

\(\displaystyle 3x+6y=15\)

Possible Answers:

\(\displaystyle (0,2.5)\)

\(\displaystyle (0,5)\)

\(\displaystyle (5,0)\)

\(\displaystyle (0,6)\)

\(\displaystyle (2.5,0)\)

Correct answer:

\(\displaystyle (0,2.5)\)

Explanation:

To find the y-intercept, let \(\displaystyle x\) equal 0.

\(\displaystyle 3(0)+6y=15\)

We can then solve for the value of \(\displaystyle y\).

\(\displaystyle 6y=15\)

\(\displaystyle y=\frac{15}{6}=2.5\)

The y-intercept will be \(\displaystyle (0,2.5)\).

Example Question #25 : How To Find X Or Y Intercept

What is the x-intercept of \(\displaystyle 2y=3x+5\)?

Possible Answers:

\(\displaystyle -\frac{5}{3}\)

\(\displaystyle \frac{6}{5}\)

\(\displaystyle -\frac{3}{5}\)

\(\displaystyle -\frac{10}{3}\)

\(\displaystyle \frac{3}{5}\)

Correct answer:

\(\displaystyle -\frac{5}{3}\)

Explanation:

To find the x-intercept, set y equal to zero and solve:

\(\displaystyle 2y=3x+5\)

\(\displaystyle 2(0)=3x+5\)

\(\displaystyle 0=3x+5\)

Subtract \(\displaystyle 5\) from both sides:

\(\displaystyle -5=3x\)

Divide both sides by \(\displaystyle 3\) to isolate x:

\(\displaystyle \frac{-5}{3}=x\)

Example Question #26 : How To Find X Or Y Intercept

What is the y-intercept of the equation?

\(\displaystyle y=\frac{2}{3}x+ 12\)

Possible Answers:

\(\displaystyle (0,4)\)

\(\displaystyle (0,8)\)

\(\displaystyle (0,3)\)

\(\displaystyle (0,12)\)

\(\displaystyle (0,0)\)

Correct answer:

\(\displaystyle (0,12)\)

Explanation:

\(\displaystyle y=\frac{2}{3}x+ 12\)

To find the y-intercept, we set the \(\displaystyle x\) value equal to zero and solve for the \(\displaystyle \small y\) value.

\(\displaystyle y= \frac{2}{3} (0) +12\)

\(\displaystyle y=12\)

Since the y-intercept is a point, we will need to convert our answer to point notation.

\(\displaystyle (0,12)\)

Example Question #93 : Algebra I

What line goes through points \(\displaystyle (-3,-7)\) and \(\displaystyle (2,3)\)?

Possible Answers:

\(\displaystyle y=-2x-4\)

\(\displaystyle y=\frac{1}{2}x-3\)

\(\displaystyle y=2x+5\)

\(\displaystyle y=2x-1\)

\(\displaystyle y=\frac{-1}{2}x+3\)

Correct answer:

\(\displaystyle y=2x-1\)

Explanation:

First, we find the slope between the two points:

\(\displaystyle P_{1}=(-3,-7)\) and \(\displaystyle P_{2}=(2,3)\)

\(\displaystyle m= \frac{y_{2} - y_{1}}{x_{2}-x_{1}}=\frac{3-(-7)}{2-(-3)}=\frac{10}{5}=2\)

Plug the slope and one point into the slope-intercept form to calculate the intercept:

\(\displaystyle y=mx+b\) 

\(\displaystyle 3=2(2)+b\) 

\(\displaystyle b=-1\)

Thus the equation between the points becomes \(\displaystyle y=2x-1\).

Example Question #1481 : High School Math

The center of a circle is \(\displaystyle (2, 4)\) and its radius is \(\displaystyle 10\). Which of the following could be the equation of the circle? 

Possible Answers:

\(\displaystyle 2x^{2} + 4y^{2} = 100\)

\(\displaystyle x^{2} + y^{2} = 100\)

\(\displaystyle (x + 2)^{2} + (y + 4)^{2} = 100\)

\(\displaystyle (x - 2)^{2} + (y - 4)^{2} = 10\)

\(\displaystyle (x - 2)^{2} + (y - 4)^{2} = 100\)

Correct answer:

\(\displaystyle (x - 2)^{2} + (y - 4)^{2} = 100\)

Explanation:

The general equation of a circle is \(\displaystyle (x - h)^{2} + (y - k)^{2} = r^{2}\), where the center of the circle is \(\displaystyle (h, k)\) and the radius is \(\displaystyle r\).

Thus, we plug the values given into the above equation to get \(\displaystyle (x - 2)^{2} + (y - 4)^{2} = 100\)

Example Question #94 : Algebra I

Which one of these equations accurately describes a circle with a center of \(\displaystyle (2,3)\) and a radius of \(\displaystyle 5\)?

Possible Answers:

\(\displaystyle x^2+y^2=25\)

\(\displaystyle (x-3)^2+(y-2)^2=25\)

\(\displaystyle (x-2)^2+(y-3)^2-25=0\)

\(\displaystyle (x^2+4)-(y^2+9)=25\)

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

Correct answer:

\(\displaystyle (x-2)^2+(y-3)^2-25=0\)

Explanation:

The standard formula for a circle is \(\displaystyle (x-a)^2+(y-b)^2=r^2\), with \(\displaystyle (a,b)\) the center of the circle and \(\displaystyle r\) the radius.

Plug in our given information.

\(\displaystyle (x-a)^2+(y-b^2)=r^2\)

\(\displaystyle (x-2)^2+(y-3)^2=25\)

This describes what we are looking for.  This equation is not one of the answer choices, however, so subtract \(\displaystyle 25\) from both sides.

\(\displaystyle (x-2)^2+(y-3)^2-25=0\)

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