# Help with finding a missing angle

#### frank.

##### New member

Could someone please explain to me how you find the missing angle in part (i) of this question? It shouldn't be too complicated because there's not a lot of marks going for it but I can't seem to figure it out. Any help would be appreciated, thanks.

#### stapel

##### Super Moderator
Staff member
View attachment 8113

Could someone please explain to me how you find the missing angle in part (i) of this question? It shouldn't be too complicated because there's not a lot of marks going for it but I can't seem to figure it out.
What have you tried? How far have you gotten? Where are you stuck?

First, what is the exercise? You posted an image, rather than typing out the text. I think the image says the following:

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From his prison cell, Fred could see the vertical prison wall XY. Fred chose a point O on his window. He marked the points A and B on the wall and ceiling of his cell such that XOA and YOB were straight lines. He measured the lengths OA, OB, and AB as 4.15m, 2.53m, and 2.72m, respectively. The points O and A were 1.65m and 1.10m respectively above the floor UV of his cell. All points lie in the same plane.

(i) Show that the size of the angle ZOA 82.38[SUP]o[/SUP], correct to two decimal places.

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I've also cleaned up the image and made it usefully viewable.