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November 9th, 2016, 01:24 PM   #1
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Please help me :)

a) 3sinx = 2,1

b) 2 + sinx = 0

c) cos³x = 0,512

d) cos²x - 3sin²x = 0

e) cos²x + 3cosx = 0
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November 9th, 2016, 01:57 PM   #2
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What are you asked to do with the equations?
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November 9th, 2016, 02:05 PM   #3
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Solve equations and check the outcome
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November 9th, 2016, 02:33 PM   #4
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Math Focus: Wibbly wobbly timey-wimey stuff.
Okay, so let's take the first one.
$\displaystyle 3~sin(x) = 2.1$

$\displaystyle sin(x) = \frac{2.1}{3}$

How do you find x from here?

-Dan
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November 24th, 2016, 08:52 AM   #5
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a) 3sin x = 2.1
sin x = 2.1/3
sin x = 0.7 (use tables for finding the value)

b) 2 + sin x = 0
sin x = -2
No solution. Because sin x range is [-1, 1].

c) cos³x = 0.512
cos x = 0.8 (use tables for finding the value)

d) cos²x - 3 sin²x = 0
1 - 4 sin²x = 0
sin x = 1/root 2 OR sin x = -1/root 2
x = n*PI + (-1)power n * (PI/4) for all n belongs to Z
OR
x = n*PI + (-1)power n * (-PI/4) for all n belongs to Z

e) cos² x + 3cos x = 0
cos x(cos x + 3) = 0
cos x = 0 or cos x = -3
cos x = 0 => x = 2n*PI for all n belongs to Z
cos x = -3 No solution. Because cos x range is [-1, 1].
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November 24th, 2016, 12:16 PM   #6
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cos x = 0 => x = 2n*PI + PI/2 for all n belongs to Z
cos x = -3 No solution. Because cos x range is [-1, 1].
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