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In the following work, two reasons are not given (in steps 1 and 5). What are these reasons?
||→FC||2 | = | FD2+CD2 | Step 1 |
| = | (||→FE||+ED)2+CD2 | Info from previous questions |
| = | ||→FE||2+2||→FE||ED+ED2+CD2 | Expanding the square |
| = | ||→FE||2+2||→FE|| ||→EC||cosθ+||→EC||2cos2θ+||→EC||2sin2θ | Info from previous questions |
| = | ||→FE||2+2||→FE|| ||→EC||cosθ+||→EC||2 | Step 5 |
| = | ||→FE||2+||→FB||2+2||→FE|| ||→FB||cosθ | Info from previous questions |
Taking the square root of both sides gives the formula for the magnitude of the sum of the vectors
→FB and
→FE:
||→FC||=√||→FE||2+||→FB||2+2||→FE|| ||→FB||cosθ.
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Pythagorean Theorem; sin2x+cos2x=1
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Pythagorean Theorem; Law of Sines
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Law of Vector Addition; Law of Cosines
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Parallelogram Law; cos2x=cos2x-sin2x