Question

∠C and ​ ∠D ​ are vertical angles. m∠C = 5x - 7 and m∠D = 8x – 55. What is m∠D ?

Answer 1

The answer is m∠D is 73.

Explanation:

In order to determine the answer, we have to know about vertical angles.

Vertical Angles are the angles opposite each other when two lines cross. These angles share the same vertex. I have attached an image that shows vertical angles.

So, according to the definition:

m∠C=m∠D

m∠C=5x-7

m∠D=8x-55

`5x-7=8x-55\\5x-8x=-55+7\\-3x=-48\\x=(-48)/(-3)\\ \\x=16`

m∠D=8*16-55=73

Finally, the angle m∠D is 73.

Answer 2

Vertical angles are the same,

Set the two equations to equal each other to solve for x:

5x-7 = 8x-55

Subtract 5x from both sides:

-7 = 3x -55

Add 55 to both sides:

3x = 48

Divide both sides by 3:

x = 48 /3

x = 16

Now you have a value for x, solve angle D:

8x -55 = 8(16) - 55 = 128 - 55 = 73 degrees.