Eric Nicholas K's answer to Wendy's Secondary Form4 Malaysia question.
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Part (a) is relatively straightforward if you know the sine and cosine rules.
Part (b) is the challenge. Here, what the statements are trying to say is that the length of CD, the length of BC and angle CDB remain unchanged.
If angle CBD is fixed, there is a limit to how we orientate lines BC and BD. Add that to the fact that length CD is unchanged, we can see that CD and part of BD must remain fixed. There is no rule, however, that says that BD must remain unchanged.
Since BC must remain unchanged, the only thing we can do is to 'rotate' BC about the pivot at C (hinged at C) such that the line cuts BD again at another point. And there we have it, the alternative triangle.
One last rule sin a = sin (180 - a) is useful here.
Part (b) is the challenge. Here, what the statements are trying to say is that the length of CD, the length of BC and angle CDB remain unchanged.
If angle CBD is fixed, there is a limit to how we orientate lines BC and BD. Add that to the fact that length CD is unchanged, we can see that CD and part of BD must remain fixed. There is no rule, however, that says that BD must remain unchanged.
Since BC must remain unchanged, the only thing we can do is to 'rotate' BC about the pivot at C (hinged at C) such that the line cuts BD again at another point. And there we have it, the alternative triangle.
One last rule sin a = sin (180 - a) is useful here.
Date Posted:
6 years ago
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