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#### Brian Bart

##### New member

- Aug 18, 2019

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- Thread starter Brian Bart
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- Thread starter
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- Aug 18, 2019

- 1

part (i) of the student's response is correct.

part (ii) has an algebra error in determining the length of DC

if $DC^2 = DB^2 - CB^2$, then $DC \ne DB - CB$

the trig for part (iii) is correct ... can't say I agree with using 120 degrees for angle ADB since it induces rounding error in determining the length of AB.

Using the equation $\sin(40) = \dfrac{BC}{AB} \implies AB = \dfrac{BC}{\sin(40)}$ will not induce that error.

part (ii) has an algebra error in determining the length of DC

if $DC^2 = DB^2 - CB^2$, then $DC \ne DB - CB$

the trig for part (iii) is correct ... can't say I agree with using 120 degrees for angle ADB since it induces rounding error in determining the length of AB.

Using the equation $\sin(40) = \dfrac{BC}{AB} \implies AB = \dfrac{BC}{\sin(40)}$ will not induce that error.

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