ΔABC has three sides with these lengths: AB = 9, BC = 40, and CA = 41. What is the value of cos C?

Mathematics

1 answer:

Effectus [21]2 years ago

6 0

From the Law of Cosines
Cos (C) = (a^2 + b^2 -c^2) / 2 * a * b
Cos (C) =(40^2 + 41^2 -9^2) / 2 * 40 * 41
Cos (C) = 1,600 + 1,681 - 81 / 3,280
Cos (C) = 3,200 / 3,280
Cos (C) = 0.9756097561 
Incidentally, Angle C = 12.68 Degrees

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The equations 3 x minus 4 y = negative 2, 4 x minus y = 4, 3 x + 4 y = 2, and 4 x + y = negative 4 are shown on the graph below.

stich3 [128]

Answer:

(–1.4, 1.5)

Step-by-step explanation:

The blue line and the purple line are the lines corresponding to the equations of interest. Their point of intersection is in the 2nd quadrant, so is nearest to ...

(–1.4, 1.5)

It can be useful to understand that for equations in standard form:

ax +by = c

the x- and y-intercepts are ...

x-intercept: c/a . . . . value of x for y = 0
y-intercept: c/b . . . . value of y for x = 0

For the equations of interest, the first has intercepts of ...

x=2/3, y=1/2 . . . . graphed line makes a 1st-quadrant triangle with the axes (blue line)

And the second has intercepts of ...

x=-1, y=-4 . . . . graphed line makes a 3rd-quadrant triangle with the axes (purple line)

Since the purple line has a steeper slope, the point of intersection of the lines will be in the 2nd quadrant. There is only one 2nd-quadrant answer choice: (-1.4, 1.5).