ACT Math : How to find out when an equation has no solution

Study concepts, example questions & explanations for ACT Math

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Example Questions

Example Question #1901 : Act Math

Given the following system, find the solution:

x = y – 2

2x – 2y = 2

Possible Answers:

(0, 0)

(0, 1)

(1, 1)

no solution

(1, 2)

Correct answer:

no solution

Explanation:

When 2 equations in a system have the same slopes, they will either have no solution or infinite solutions. Since the y-intercepts are not the same, there is no solution to this system.

Example Question #1 : How To Find Out When An Equation Has No Solution

Solve for \(\displaystyle x\):

\(\displaystyle 27x-32=-(-27x+27)\)

Possible Answers:

\(\displaystyle 5\)

No solution

\(\displaystyle 1.1\)

\(\displaystyle -9.25\cdot 10^{-2}\)

Infinite Solutions 

Correct answer:

No solution

Explanation:

\(\displaystyle 27x-32=-(-27x+27)\)

Like other "solve for x" problems, to begin it, the goal is to get x by itself on one side of the equals sign. In this problem, before doing so, the imaginary -1 in front of (-27x+27) must be distributed. 

\(\displaystyle 27x-32=27x-27\)

Once this is done, you may start to try to get x by itself.

\(\displaystyle {\color{Red} 27x}-32={\color{Red} 27x}-27\)

However, when subtracting 27x from either side and doing the same on the other,  the 27x term cancels out. As a result, the equation becomes:

\(\displaystyle -32=-27\)

We know this is an untrue statement because these numbers are 5 spaces away from each other on the number line. The final answer is No Solution

\(\displaystyle -32\neq-27\)

Example Question #1 : How To Find Out When An Equation Has No Solution

Given the following system, find the solution:

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

\(\displaystyle 3y - 5 = 6x\)

Possible Answers:

\(\displaystyle (0, 3)\)

\(\displaystyle \left (- \frac{5}{6}, 0 \right )\)

No solution

\(\displaystyle \left (- \frac{2}{3}, 0 \right )\)

\(\displaystyle \left (0, \frac{5}{3} \right )\)

Correct answer:

No solution

Explanation:

When two equations have the same slope, they will have either no solution or infinite solutions.  By putting both equations into the form \(\displaystyle y = mx +b\), we get:

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

and

\(\displaystyle y = 2x +\frac{5}{3}\)

With the equations in this form, we can see that they have the same slope, but different y-intercepts.  Therefore, there is no solution to this system.

Example Question #3 : How To Find Out When An Equation Has No Solution

Solve the following equation for \(\displaystyle x\):

\(\displaystyle 2\left ( x - 4\right ) = \frac{4x + 5}{2}\)

Possible Answers:

No solution

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

\(\displaystyle 0\)

\(\displaystyle \frac{13}{2}\)

Infinite solutions

Correct answer:

No solution

Explanation:

In order to solve for \(\displaystyle x\), we must get \(\displaystyle x\) by itself on one side of the equation.

\(\displaystyle 2\left ( x - 4\right ) = \frac{4x + 5}{2}\)

First, we can distribute the \(\displaystyle 2\) on the left side of the equal sign and the \(\displaystyle \frac{1}{2}\) on the right side.

\(\displaystyle 2x - 8= 2x +\frac{ 5}{2}\)

When we try to get \(\displaystyle x\) by itself, the \(\displaystyle 2x\) terms on each side of the equation cancel out, leaving us with:

\(\displaystyle - 8= \frac{ 5}{2}\)

We know this is an untrue statement, so there is no solution to this equation.

Example Question #1 : How To Find Out When An Equation Has No Solution

Find the solution to the following equation if x = 3: 

y = (4x2 - 2)/(9 - x2)

Possible Answers:

3

6

no possible solution

0

Correct answer:

no possible solution

Explanation:

Substituting 3 in for x, you will get 0 in the denominator of the fraction. It is not possible to have 0 be the denominator for a fraction so there is no possible solution to this equation.

Example Question #3 : How To Find Out When An Equation Has No Solution

Nosol1

Possible Answers:

3

–1/2

–3

1

There is no solution

Correct answer:

There is no solution

Explanation:

Nosol2

Example Question #4 : How To Find Out When An Equation Has No Solution

\(\displaystyle \small h\left ( x\right )=\frac{28}{x+4}\)  

\(\displaystyle \small \textup{For which of the following values of}\,x\,\textup{is the above function undefined?}\)

Possible Answers:

None of the other answers

\(\displaystyle \small 4\)

\(\displaystyle \small -4\)

\(\displaystyle \small 0\)

\(\displaystyle \small 28\)

Correct answer:

\(\displaystyle \small -4\)

Explanation:

A fraction is considered undefined when the denominator equals 0. Set the denominator equal to zero and solve for the variable.

\(\displaystyle \small x+4=0\)

\(\displaystyle \small x=-4\)

Example Question #131 : Equations / Inequalities

\frac{x+2}{3}=\frac{x}{3}\(\displaystyle \frac{x+2}{3}=\frac{x}{3}\) Solve for \(\displaystyle x\).

Possible Answers:

\(\displaystyle 3\)

\(\displaystyle -2\)

\(\displaystyle 4\)

No solutions.

\(\displaystyle -3\)

Correct answer:

No solutions.

Explanation:

Cross multiplying leaves \(\displaystyle 3x+6=3x\), which is not possible.

Example Question #2 : How To Find Out When An Equation Has No Solution

Undefined_denom3

 

I.  x = 0

II. x = –1

III. x = 1

Possible Answers:

II and III only

II only

I only

I, II, and III

III only

Correct answer:

I only

Explanation:

 Undefined_denom2

Example Question #2 : How To Find Out When An Equation Has No Solution

Solve: 

\(\displaystyle 3(2x - 6) + 2x = 7x - 12\)

Possible Answers:

\(\displaystyle 6\)

\(\displaystyle -30\)

\(\displaystyle 10\)

\(\displaystyle 30\)

\(\displaystyle -6\)

Correct answer:

\(\displaystyle 6\)

Explanation:

First, distribute, making sure to watch for negatives. 

\(\displaystyle 3(2x - 6) + 2x = 7x - 12\)

\(\displaystyle 6x - 18 + 2x = 7x - 12\)

Combine like terms. 

\(\displaystyle 8x - 18 = 7x - 12\)

Subtract 7x from both sides. 

\(\displaystyle x - 18 = -12\)

Add 18 on both sides and be careful adding integers. 

\(\displaystyle x = 6\)

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