Dave's ESL Cafe's Student Discussion Forums

[river1974]

Dear teachers:

(a) The impinging direction of the light rays from the different sources is required to be maintained perpendicularly to the projection direction of the projector system.
(b) The impinging direction of the light rays from the different sources is required to be maintained perpendicular to the projection direction of the projector system.

Which one is correct?

Thanks.

[lotus]

Hi river1974,

B is more correct.

You might shorten the sentence and re-write as:

The direction of impinging light rays from other sources must be maintained (perpendicular) to the projection system.

The words in parenthesis can be replaced with "at 90 degrees" or "at a right angle."


--lotus

[pavilion]

(B) is the right one.

[river1974]

Thanks. Here comes another question. Which one is more natural: at forty-five degrees or at forty five degrees?

[pavilion]

At forty-five degrees is the correct way.