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Given: ∠AOC, ∠BOC - complementary angles

m∠AOC = m∠BOC +30°
Find: m∠AOC, m∠BOC
Fill in the chart:
Statement Reason
AOC+ COB = 90 Complementary angles
BOC + (put answer here) + (put answer here) = 90 Subsitution
BOC=30 Algebra
AOC=60 Algebra

Given: ∠AOC, ∠BOC - complementary angles m∠AOC = m∠BOC +30° Find: m∠AOC, m∠BOC Fill-example-1
User Sapanda
by
8.0k points

1 Answer

1 vote

Answer:

  • 30
  • COB . . . . or . . . . BOC

Explanation:

The reason given on the line of interest is "substitution," so the problem boils down to determining what was substituted for what. The previous statement says ...

AOC + COB = 90

and the first part of the statement we're to complete has BOC + ___.

We see from the given statements that m∠AOC = m∠BOC + 30°, so it appears that is the substitution that has been made: AOC has been replaced by BOC + 30.

This means the first blank is filled with 30.

__

The second part of the previous statement is ...

AOC + COB = 90

so we believe this (COB) should go in the second blank.

__

Then the line of interest would read ...

BOC + 30 + COB = 90

_____

Comment on the problem

There is a curious mix of notations here. Usually, (as in the beginning of this problem) we refer to the measure of an angle using "m∠" in front of the angle designator, and we use a degree symbol to indicate the units of that measure. Part-way through the problem statement written here, those notations were dropped, and we're to assume they are intended. IMO, this is a poor way to demonstrate careful problem solving.

The substitution given for AOC is BOC+30, but the line into which that is substituted has AOC +COB = 90. This means the equation after substitution is ...

BOC +30 +COB = 90

Since BOC and COB are the same angle, we can sort of fudge the "algebra" to get to BOC=30, but if the problem were more carefully written, the angle would be referred to by consistent nomenclature:

m∠AOC + m∠BOC = 90° . . . . . . . . . preferred angle designations

(m∠BOC + 30°) + m∠BOC = 90° . . . . substitution for m∠AOC

2(m∠BOC) = 60° . . . . . . algebra (subtract 30°, collect terms)

m∠BOC = 30° . . . . . . . . algebra (divide by 2)

User Michael Scheper
by
7.3k points
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