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Three Unknowns

Solve these sets of three simultaneous, linear equations to find the values of the variables
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This is level 1: Standard set of questions with the equations set out in a familiar way. You will be awarded a trophy if you get at least 15 answers correct and you do this activity online.

1

\(2x+y-3z= -8 \\ 3x+y+z= 14 \\ x-y+2z = 9\)

\(x = \) ✓ ✗ ☐ \(y = \) ✓ ✗ ☐ \(z = \) ✓ ✗

2

\( 5a+2b+c=45 \\ 3a+4b+2c= 48 \\ a+5b+c=39\)

\(a = \) ✓ ✗ ☐ \(b = \) ✓ ✗ ☐ \(c = \) ✓ ✗

3

\(2d+3e-4f = 11 \\ d-e-f= -6\\ 9d+2e-2f=65\)

\(d = \) ✓ ✗ ☐ \(e = \) ✓ ✗ ☐ \(f = \) ✓ ✗

4

\( g-7h-7i=-73 \\ 2g-2h+i= -2\\ 5g+3h+i = 45\)

\(g = \) ✓ ✗ ☐ \(h = \) ✓ ✗ ☐ \(i = \) ✓ ✗

5

\( j+k+l= 16 \\ 2j-3k+9l= 28\\ -j+k-3l=-12\)

\(j = \) ✓ ✗ ☐ \(k = \) ✓ ✗ ☐ \(l = \) ✓ ✗

6

\( -m+4n-p=-2 \\ 2m-3n+5p= 46\\ 7m-n+p=41\)

\(m = \) ✓ ✗ ☐ \(n = \) ✓ ✗ ☐ \(p = \) ✓ ✗

7

\( 2q+2r-5s=32 \\ q-r+2s= -12\\ -q+5r+5s=-60\)

\(q = \) ✓ ✗ ☐ \(r = \) ✓ ✗ ☐ \(s = \) ✓ ✗

8

\( t-5u-5v=-13 \\ 2t+u+3v= -8\\ -5t+5u-v=37\)

\(t = \) ✓ ✗ ☐ \(u = \) ✓ ✗ ☐ \(v = \) ✓ ✗

9

\( 9w+x-y=7 \\ 2w+7x-3y= -37\\ -7w+5x+5y=21\)

\(w = \) ✓ ✗ ☐ \(x = \) ✓ ✗ ☐ \(y = \) ✓ ✗

10

\( 8x-5y+2z=-26 \\ -3x+7y-z= 53\\ 2z-5x-y=-46\)

\(x = \) ✓ ✗ ☐ \(y = \) ✓ ✗ ☐ \(z = \) ✓ ✗

Check

This is Three Unknowns level 1. You can also try:
Level 2 Level 3

Instructions

Try your best to answer the questions above. Type your answers into the boxes provided leaving no spaces. As you work through the exercise regularly click the "check" button. If you have any wrong answers, do your best to do corrections but if there is anything you don't understand, please ask your teacher for help.

When you have got all of the questions correct you may want to print out this page and paste it into your exercise book. If you keep your work in an ePortfolio you could take a screen shot of your answers and paste that into your Maths file.
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Description of Levels

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Two unknowns - You really should start here before taking on three unknowns.

Level 1 - Standard set of questions with the equations set out in a familiar way

Level 2 - A mixed up collection of equations to challenge the high achiever

Level 3 - An awful heap of tedious equations generated by AI where the solutions are vulgar fractions (not recommended)

More on this topic including lesson Starters, visual aids, investigations and self-marking exercises.

Answers to this exercise are available lower down this page when you are logged in to your Transum account. If you don’t yet have a Transum subscription one can be very quickly set up if you are a teacher, tutor or parent.

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Help

The video above is from Corbett Maths.

Example using matrix row reduction:

Solve the following system of equations:

$$x+y+z=3$$ $$2x-y+z=0$$ $$x-2y-z=-3$$

We begin by writing the augmented matrix for the system of equations:

$$\left[\begin{array}{ccc|c}1 & 1 & 1 & 3\\2 & -1 & 1 & 0\\1 & -2 & -1 & -3\end{array}\right]$$

We now perform row operations to transform this matrix into echelon form:

\(R2 = R2 - 2 \times R1\)

$$\left[\begin{array}{ccc|c}1 & 1 & 1 & 3\\0 & -3 & -1 & -6\\1 & -2 & -1 & -3\end{array}\right]$$

\(R3 = R3 - R1\)

$$\left[\begin{array}{ccc|c}1 & 1 & 1 & 3\\0 & -3 & -1 & -6\\0 & -3 & -2 & -6\end{array}\right]$$

\(R3 = R3 - R2\)

$$\left[\begin{array}{ccc|c}1 & 1 & 1 & 3\\0 & -3 & -1 & -6\\0 & 0 & -1 & 0\end{array}\right]$$

The augmented matrix is now in the form:

$$\left[\begin{array}{ccc|c}a & b & c & d\\0 & e & f & g\\0 & 0 & h & i\end{array}\right]$$

If \( h \neq 0\) there is a unique solution.

If \( h = 0 \text{ and } i \neq 0 \) there is no solution

If \( h = 0 \text{ and } i = 0 \) there are infinitely many solutions (let \(z=t\)).

In the example above ...

from \(R3\) it can be seen that \( z=0 \)

from \(R2\) it can be seen that \( y=2 \)

from \(R1\) it can be seen that \( x=1 \)

The solutions are \( x=1,y=2,z=0 \).

Don't wait until you have finished the exercise before you click on the 'Check' button. Click it often as you work through the questions to see if you are answering them correctly. You can double-click the 'Check' button to make it float at the bottom of your screen.

Answers to this exercise are available lower down this page when you are logged in to your Transum account. If you don’t yet have a Transum subscription one can be very quickly set up if you are a teacher, tutor or parent.

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