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mr_godi [17]
3 years ago
12

Prove the identity: 2sin(a+b)sin(a-b) = cos(2b)-cos(2a)

Mathematics
2 answers:
Aleonysh [2.5K]3 years ago
4 0

2sin(a+b)sin(a-b)=cos(2b)-cos(2a) \\\\[-0.35em] ~\dotfill\\\\ \stackrel{\textit{let's do this part first, we'll add the "2" later}}{sin(a+b)sin(a-b)} \\\\\\ \underset{\textit{difference of squares}}{[sin(a)cos(b)+cos(a)sin(b)][sin(a)cos(b)-cos(a)sin(b)]} \\\\\\ sin^2(a)cos^2(b)-cos^2(a)sin^2(b) \\\\[-0.35em] \rule{34em}{0.25pt}\\\\ \stackrel{\textit{we know that}}{cos(2\theta )=cos^2(\theta)-sin^2(\theta)}\implies sin^2(\theta)=cos^2(\theta)-cos(2\theta ) \\\\[-0.35em] \rule{34em}{0.25pt}

[cos^2(a)-cos(2a)]cos^2(b)-cos^2(a)[cos^2(b)-cos(2b)] \\\\\\ \underline{cos^2(a)cos^2(b)}-cos(2a)cos^2(b)\underline{-cos^2(a)cos^2(b)}+cos^2(a)cos(2b) \\\\\\ cos^2(a)cos(2b)-cos(2a)cos^2(b) \\\\[-0.35em] \rule{34em}{0.25pt}\\\\ \stackrel{\textit{we also know that}}{cos(2\theta)=2cos^2(\theta)-1}\implies \cfrac{cos(2\theta)+1}{2}=cos^2(\theta) \\\\[-0.35em] \rule{34em}{0.25pt}

\left[ \cfrac{cos(2a)+1}{2} \right]cos(2b)-cos(2a)\left[ \cfrac{cos(2b)+1}{2} \right] \\\\\\ \stackrel{\textit{now let's bring back the "2"}}{2\left( \left[ \cfrac{cos(2a)+1}{2} \right]cos(2b)-cos(2a)\left[ \cfrac{cos(2b)+1}{2} \right] \right)} \\\\\\\ [cos(2a)+1]cos(2b)-cos(2a)[cos(2b)+1] \\\\\\ \underline{cos(2a)cos(2b)}+cos(2b)-\underline{cos(2a)cos(2b)}-cos(2a)\implies cos(2b)-cos(2a)

Alex777 [14]3 years ago
3 0

Answer:

see below

Step-by-step explanation:

see attached for my workings, step-by-step and the trig identities I used.

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Sharon is 54 inches tall. tree in her backyard is five times as tall as she is. the floor of her treehouse is at a height that i
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Circle A has center (0, 0) and radius 3. Circle B has center (-5, 0) and radius 1. What sequence of transformations could be use
Dmitrij [34]

A translation of T(x, y) = (- 5, 2) and a dilation with center (- 5, 2) with a scale factor of 1 / 3 are necessary to transform circle A into circle B. (Correct choice: D)

<h3>What sequence of rigid transformations can be done on a circle</h3>

In this problem we must determine the sequence of transformations require to transform circle A into circle B. From analytical geometry we know that the equation of the circle in standard form is:

(x - h)² + (y - k)² = r²

Where:

  • (h, k) - Coordinates of the center.
  • r - Radius of the circle.

Then, we need to apply the following rigid transformations:

Translation

f(x, y) → f(x - h, y - k), where (h, k) is the translation vector.

Dilation with center at the center of the circle

r → k · r, where k is the scale factor.

The circle A is represented by x² + y² = 3, then we derive the expression for the circle B:

f(x, y) → f(x + 5, y - 2)

(x + 5)² + (y - 2)² = 9

r → k · r

(x + 5)² + (y - 2)² = (1 / 3)² · 9

(x + 5)² + (y - 2)² = 1

Then, a translation of T(x, y) = (- 5, 2) and a dilation with center (- 5, 2) are necessary to transform circle A into circle B.

To learn more on rigid transformations: brainly.com/question/28004150

#SPJ1

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