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LA and LB are vertical angles. If mLA=(x+21)° and mLB=(4x-30)°, the find then measure of LB

User Jackysee
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1 Answer

6 votes

Answer:

38 degrees

Explanation:

Vertical angles are congruent(equal measures), so mLA = mLB

STEP 1:

Let's use some simple substitution.

mLA = mLB

mLA = x+21, mLB = 4x-30

You plug these two in and get:

x+21 = 4x-30

This is your equation.

STEP 2:

Let's solve our equation!

x+21 = 4x-30

(add 30 to both sides)

x+51 = 4x

(subtract x from both sides)

51 = 3x

(switch order for comprehension)

3x = 51

(divide both sides by 3)

x = 17

Ta-da! You get the measure of x = 17 degrees.

STEP 3:

Let's plug in our value of x to get the value of LB.

mLB = 4x - 30

mLB = 4(17) - 30

mLB = 68 - 30

mLB = 38

This is your answer.

User Ale Plo
by
8.3k points

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