Big Ideas Math Integrated I, 2016
BI
Big Ideas Math Integrated I, 2016 View details
3. Postulates and Diagrams
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Exercise 18 Page 463

Do we know how the two planes intersect?

No.

Practice makes perfect
Consider the angle of intersection — which we can think of as ∠ PLK — between the two planes in the diagram.

Nowhere in the diagram are we given any information about the measure of this angle of intersection. Therefore, we cannot assume that ∠ PLK is a right angle.