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Two angles are complementary. The larger angle is 6° less than five times the measure of the smaller angle. What is the measure of the larger angle?
63°
87°
74°
66°
74°
Use the options: Since the larger angle is 5×smaller−6, adding 6 to each option should make the result divisible by 5. For 74, 74+6=80, and 80/5=16 (smaller angle). 74+16=90, which satisfies the complementary condition.
Two angles are complementary, meaning their sum is 90 degrees. The larger angle is 6 degrees less than five times the smaller angle.
x+y=90, y=5x−6
Use the options: Since the larger angle is 5×smaller−6, adding 6 to each option should make the result divisible by 5. For 74, 74+6=80, and 80/5=16 (smaller angle). 74+16=90, which satisfies the complementary condition.
Students often solve for the smaller angle (16°) instead of the larger angle (74°) requested in the question.
Define the variables
Let the smaller angle be x and the larger angle be y. Since they are complementary, their sum is 90°.
x+y=90
Set up the second equation
According to the problem, the larger angle y is 6 degrees less than five times the smaller angle x.
y=5x−6
Substitute and solve for x
Substitute y in the first equation: x+(5x−6)=90. Combining terms gives 6x−6=90, so 6x=96.
x=696=16°
Calculate the larger angle y
Using the value of x, find y: y=90−16=74°. Alternatively, y=5(16)−6=80−6=74°.
y=74°
C is correct because the smaller angle is 16° and the larger angle is 74°, which sum to 90° and satisfy the given condition.
This concept of complementary (90°) and supplementary (180°) angles frequently appears in Geometry and Trigonometry problems involving angle identities.