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Natalija [7]
3 years ago
13

By writing sin 3x = sin(2x+x), show that sin 3x = 3 sin x - 4 sin^3 x.

Mathematics
1 answer:
Ksju [112]3 years ago
8 0

Given the trigonometry expression:

sin 3x = sin(2x+x),

In trigonometry identity;

Sin(A+B) = sinAcosB + cosAsinB

The expression above will then become;

sin(2x+x) =sin2xcosx+cos2xsinx\\sin(2x+x) =2sinxcosxcosx + (1-2sin^2x)sinx\\sin(2x+x) =2sinxcos^2x + (1-2sin^2x)sinx\\

Recall that sin^2x + cos^x = 1, hence;

sin(2x+x) =2sinx(1-sin^2x)+ (1-2sin^2x)sinx\\Expand\\sin(2x+x) =2sinx-2sin^3x+ sinx-2sin^3x\\sin(2x+x) =2sinx + sinx-2sin^3x-2sin^3x\\sisn(2x+x) = 3sinx-4sin^3x

This shows that sin3x =3sinx-4sin^3x (Proved!)

Learn more here: brainly.com/question/7331447

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