Question

Cos2a,если sina=-4/1

Answer 1

Cos2a=1-2sin2a
Sin2a=1/16
Cos2a=1-1/16=1/15
наверно вы имели ввиду -1/4?

Answer 2

Given that sina=-4/1, we can use the Pythagorean identity sin^2a + cos^2a = 1 to find cosa.

First, let's find sin^2a:

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sin^2a = (-4/1)^2 = 16/1 = 16

Next, we can use the Pythagorean identity to find cos^2a:

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sin^2a + cos^2a = 1
16 + cos^2a = 1
cos^2a = 1 - 16
cos^2a = -15

Since cos^2a is negative, we know that cos a is imaginary, and therefore cos 2a is also imaginary. So, the value of cos 2a is:

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cos 2a = cos^2a - sin^2a
       = -15 - 16
       = -31

Therefore, cos 2a is -31.