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3 years ago

Calculate the value of the following determinants: | 1 -1 3 2 5 0 -3 1 2 | and | -1 -8 2 9 1 0 4 1 2 |

Mathematics

1 answer:

vitfil [10]3 years ago

6 0

Answer:

1) The determinant = 65

2) The determinant = 152

Step-by-step explanation:

Let us show how to find the determinant of a matrix

You can find the determinant of this Matrix $\left[\begin{array}{ccc}a&b&c\\d&e&f\\g&m&n\end{array}\right]$

by using this rule

Determinant = a(en - fm) - b(dn - fg) + c(dm - eg)

Let us use this rule with the given matrices

$\left[\begin{array}{ccc}1&-1&3\\2&5&0\\-3&1&2\end{array}\right]$

The determinand = 1[(5)(2) - (0)(1)] - (-1)[(2)(2) - (0)(-3)] + 3[(2)(1) - 5(-3)]

= 1[10 - 0] - (-1)[4 - 0] + 3[2 - (-15)]

= 1[10] + 1[4] + 3[2+15]

= 10 + 4 + 3[17]

= 10 + 4 + 51

= 65

The determinant = 65

Let us do the second one

$\left[\begin{array}{ccc}-1&-8&2\\9&1&0\\4&1&2\end{array}\right]$

The determinand = -1[(1)(2) - (0)(1)] - (-8)[(9)(2) - (0)(4)] + 2[(9)(1) - 1(4)]

= -1[2 - 0] - (-8)[18 - 0] + 2[9 - 4]

= -1[2] + 8[18] + 2[5]

= -2 + 144 + 10

= 152

The determinant = 152

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Two lighthouses are located 75 miles from one another on a north-south line. If a boat is spotted S 40o E from the northern ligh

yuradex [85]

Answer:

The northern lighthouse is approximately $24.4\; \rm mi$ closer to the boat than the southern lighthouse.

Step-by-step explanation:

Refer to the diagram attached. Denote the northern lighthouse as $\rm N$ , the southern lighthouse as $\rm S$ , and the boat as $\rm B$ . These three points would form a triangle.

It is given that two of the angles of this triangle measure $40^{\circ}$ (northern lighthouse, $\angle {\rm N}$ ) and $21^{\circ}$ (southern lighthouse $\angle {\rm S}$ ), respectively. The three angles of any triangle add up to $180^{\circ}$ . Therefore, the third angle of this triangle would measure $180^{\circ} - (40^{\circ} + 21^{\circ}) = 119^{\circ}$ (boat $\angle {\rm B}$ .)

It is also given that the length between the two lighthouses (length of $\rm NS$ ) is $75\; \rm mi$ .

By the law of sine, the length of a side in a given triangle would be proportional to the angle opposite to that side. For example, in the triangle in this question, $\angle {\rm B}$ is opposite to side $\rm NS$ , whereas $\angle {\rm S}$ is opposite to side ${\rm NB}$ . Therefore:

$\begin{aligned} \frac{\text{length of NS}}{\sin(\angle {\rm B})} = \frac{\text{length of NB}}{\sin(\angle {\rm S})} \end{aligned}$ .

Substitute in the known measurements:

$\begin{aligned} \frac{75\; \rm mi}{\sin(119^{\circ})} = \frac{\text{length of NB}}{\sin(21^{\circ})} \end{aligned}$ .

Rearrange and solve for the length of $\rm NB$ :

$\begin{aligned} & \text{length of NB} \\ =\; & (75\; \rm mi) \times \frac{\sin(21^{\circ})}{\sin(119^{\circ})} \\ \approx\; & 30.73\; \rm mi\end{aligned}$ .

(Round to at least one more decimal places than the values in the choices.)

Likewise, with $\angle {\rm N}$ is opposite to side ${\rm SB}$ , the following would also hold:

$\begin{aligned} \frac{\text{length of NS}}{\sin(\angle {\rm B})} = \frac{\text{length of SB}}{\sin(\angle {\rm N})} \end{aligned}$ .

$\begin{aligned} \frac{75\; \rm mi}{\sin(119^{\circ})} = \frac{\text{length of SB}}{\sin(40^{\circ})} \end{aligned}$ .

$\begin{aligned} & \text{length of SB} \\ =\; & (75\; \rm mi) \times \frac{\sin(40^{\circ})}{\sin(119^{\circ})} \\ \approx\; & 55.12\; \rm mi\end{aligned}$ .

In other words, the distance between the northern lighthouse and the boat is approximately $30.73\; \rm mi$ , whereas the distance between the southern lighthouse and the boat is approximately $55.12\; \rm mi$ . Hence the conclusion.