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CCSS.Math:

what is the measure of angle C Oh B so this is C this is oh and this is B so they're telling us what is the measure of this angle right over here this is angle this is angle C OB and they clearly don't give it to us we need to figure it out and what they do give us is they give us the measure of an adjacent angle this angle this 45-degree angled angle D Oh C is adjacent because it shares it shares this arm this this segment OC with angle C Oh B and then they give us the combined angle if you take the two outer arms of the two angle that these two outer segments if you look at angle B OD they tell us that that is 70 degrees so if the measure of the angle made from these two the two outer arms of these two adjacent angles the two outer rays if you kept going out like this if that's 70 degrees and one of the adjacent angles is 45 then this one right over here must be 70 minus 45 or another way of thinking about it is this angle the question mark angle plus 45 degrees plus 45 degrees must be equal to 70 degrees must be equal to 70 degrees or that question mark must be equal to must be equal to 70 degrees minus 45 degrees minus 45 degrees so what's this going to be well if it was 70 minus 40 we'd get 230 but then we have to subtract another five so it's going to be 25 degrees so the measure of angle C OB is 25 degrees