# F.4 Maths Trigonometry(2)

question: http://postimg.org/image/6818gavb5/

solution: http://postimg.org/image/l2ptuh4w1/

For part(c), I think that VE should be the projection of VC on VBD.

But why in the solution, it adds a point H and the required angle becomes angle

HVC.

What is/are the mistake(s) I have made?

RE Toi Lam:

So actually CE is not 丄 BED?

We should calculate the shortest distance additionally if the base is not square?

### 1 個解答

• 最佳解答

It is because the right pyramid has a rectangular base but not square base.

CE is 丄 to VE but CE is not the shortest distance to plane VBD (or you can say the line BED)

As you see in the solution, CH is the shortest distance which is 丄 to BED.

2015-06-11 17:28:17 補充：

CE is not 丄 BED (as you see in the solution)

We should calculate the shortest distance additionally if the base is not square.

2015-06-11 17:32:53 補充：

Just think about the properties of rectangle and square.

When diagonals are drawn on rectangle and square, the 4 angles at the middle are 90° when it is square but rectangle's are not.

(right pyramid means the apex is directly above the center of the base.)

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