2017 Maths AS/A Levels
Reasoning
The postcard shows 2 congruent rectangles, each containing two pairs of congruent rightangled triangles.
Explain why the angle marked α + β is the sum of the marked angles in the blue and red
triangles.
Explain why the orange parallelogram has area sin (α + β ) and that the two orange
rectangles have a total area of sin α cos β + cos α sin β .
Compare this with other proofs you know of this formula.
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AE 05/04/2016
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