-13=r/9+8
What's r stand for? I need help!

r is usually the radius but can also be a variable, in this case r = -189

Step-by-step explanation:

Solve for r:

-13 = r/9 + 8

Put each term in r/9 + 8 over the common denominator 9: r/9 + 8 = r/9 + 72/9:

-13 = r/9 + 72/9

r/9 + 72/9 = (r + 72)/9:

-13 = (r + 72)/9

-13 = (r + 72)/9 is equivalent to (r + 72)/9 = -13:

(r + 72)/9 = -13

Multiply both sides of (r + 72)/9 = -13 by 9:

(9 (r + 72))/9 = -13×9

(9 (r + 72))/9 = 9/9×(r + 72) = r + 72:

r + 72 = -13×9

9 (-13) = -117:

r + 72 = -117

Subtract 72 from both sides:

r + (72 - 72) = -72 - 117

72 - 72 = 0:

r = -72 - 117

-72 - 117 = -189:

r = -189

we have three similar triangles, because each has a right angle and shares an angle.   let's write the angles in order: opposite to short leg, long leg, hypotenuse.

cab similar to bad similar to cbd

or as ratios,

ca: ab: cb = ba: ad: bd = cb: bd: cd

we also know

ac = ad + cd

(ad+cd): ab: cb = ba: ad: bd = cb: bd: cd

(ad+cd)/cb=cb/cd

we have cb=6, ad=5 and seek x=cd.

we reject the negative root and conclude x=4

answer: 4