Given

we have

Squaring both sides, we have

And finally

Note that, when we square both sides, we have to assume that

because we're assuming that this fraction equals a square root, which is positive.
So, if that fraction is positive you'll actually have roots: choose

and you'll have

Which is a valid solution. If, instead, the fraction is negative, you'll have extraneous roots: choose

and you'll have

Squaring both sides (and here's the mistake!!) you'd have

which is not a solution for the equation, if we plug it in we have

Which is clearly false
Answer:
Using the Angle Addition Postulate, 20 + m∠DBC = 80. So, m∠DBC = 60° using the subtraction property of equality.
Step-by-step explanation:
If point D is the interior of angle ABC, then the angle addition postulate theory states that the sum of angle ABD and angle DBC is equals to angle ABC. The angle addition postulate is used to measure the resulting angle from two angles placed side by side.
From the attached image, ∠ABD and ∠DBC are placed side by side to form ∠ABC. Given that m∠ABD = 20° and m∠ABC = 80°
Hence, using angle addition postulate:
m∠ABD + m∠DBC = m∠ABC
20 + m∠DBC = 80
subtracting 20 from both sides (subtraction property of equality)
m∠DBC = 80 - 20
m∠DBC = 60°
Answer:
D
Step-by-step explanation:
I took the quiz :)
Divide 42 by 30 and that should be your correct answer.
hope this helps.